Add CC dark theme option

This commit adds an option to enable a dark theme in the Community
Console. It can be enabled manually with a switch which is injected in
the CC or automatically by syncing it with the OS dark mode setting.

Change-Id: I7506e80a409c5b0190d942c9de88354b6c0cce10
diff --git a/src/_locales/ca/messages.json b/src/_locales/ca/messages.json
index 7a24358..d76a7cb 100644
--- a/src/_locales/ca/messages.json
+++ b/src/_locales/ca/messages.json
@@ -63,6 +63,18 @@
     "message": "Incrementa el contrast entre els fils llegits i no llegits a la Consola de la Comunitat.",
     "description": "Feature checkbox in the options page"
   },
+  "options_ccdarktheme": {
+    "message": "Activa el tema fosc a la Consola de la Comunitat, controlat per <span id='ccdarktheme_mode--container'></span>.",
+    "description": "Feature checkbox in the options page"
+  },
+  "options_ccdarktheme_mode_switch": {
+    "message": "un botó a la consola",
+    "description": "Select option added in #ccdarktheme_mode--container, in the options_ccdarktheme string"
+  },
+  "options_ccdarktheme_mode_system": {
+    "message": "la configuració del mode fosc del SO",
+    "description": "Select option added in #ccdarktheme_mode--container, in the options_ccdarktheme string"
+  },
   "options_profileindicator_header": {
     "message": "Punt indicador",
     "description": "Heading for the profile indicator feature options"
@@ -126,5 +138,9 @@
   "inject_profileindicatoralt_numposts": {
     "message": "Nombre de preguntes i respostes en els $1 darrers mesos.",
     "description": "Tooltip for the profile indicator dot."
+  },
+  "inject_ccdarkmode_helper": {
+    "message": "Canviar tema",
+    "description": "Tooltip for the dark mode switch."
   }
 }
diff --git a/src/_locales/en/messages.json b/src/_locales/en/messages.json
index b031666..de6f351 100644
--- a/src/_locales/en/messages.json
+++ b/src/_locales/en/messages.json
@@ -67,6 +67,18 @@
     "message": "Increase contrast between read and unread threads in the Community Console.",
     "description": "Feature checkbox in the options page"
   },
+  "options_ccdarktheme": {
+    "message": "Enable the dark theme in the Community Console, controlled <span id='ccdarktheme_mode--container'></span>.",
+    "description": "Feature checkbox in the options page"
+  },
+  "options_ccdarktheme_mode_switch": {
+    "message": "with a switch in the CC",
+    "description": "Select option added in #ccdarktheme_mode--container, in the options_ccdarktheme string"
+  },
+  "options_ccdarktheme_mode_system": {
+    "message": "by the OS dark mode setting",
+    "description": "Select option added in #ccdarktheme_mode--container, in the options_ccdarktheme string"
+  },
   "options_profileindicator_header": {
     "message": "Indicator dot",
     "description": "Heading for the profile indicator feature options"
@@ -126,5 +138,9 @@
   "inject_profileindicatoralt_numposts": {
     "message": "Number of questions and replies in the last $1 months.",
     "description": "Tooltip for the profile indicator dot."
+  },
+  "inject_ccdarktheme_helper": {
+    "message": "Switch theme",
+    "description": "Tooltip for the dark mode switch."
   }
 }
diff --git a/src/_locales/es/messages.json b/src/_locales/es/messages.json
index d1103c1..bdb20af 100644
--- a/src/_locales/es/messages.json
+++ b/src/_locales/es/messages.json
@@ -63,6 +63,18 @@
     "message": "Incrementa el contraste entre los hilos leídos y no leídos en la Consola de la Comunidad.",
     "description": "Feature checkbox in the options page"
   },
+  "options_ccdarktheme": {
+    "message": "Activa el tema oscuro en la Consola de la Comunidad, controlado por <span id='ccdarktheme_mode--container'></span>.",
+    "description": "Feature checkbox in the options page"
+  },
+  "options_ccdarktheme_mode_switch": {
+    "message": "un botón en la consola",
+    "description": "Select option added in #ccdarktheme_mode--container, in the options_ccdarktheme string"
+  },
+  "options_ccdarktheme_mode_system": {
+    "message": "la configuración del modo oscuro del SO",
+    "description": "Select option added in #ccdarktheme_mode--container, in the options_ccdarktheme string"
+  },
   "options_profileindicator_header": {
     "message": "Punto indicador",
     "description": "Heading for the profile indicator feature options"
@@ -126,5 +138,9 @@
   "inject_profileindicatoralt_numposts": {
     "message": "Número de preguntas y respuestas en los últimos $1 meses.",
     "description": "Tooltip for the profile indicator dot."
+  },
+  "inject_ccdarktheme_helper": {
+    "message": "Cambiar tema",
+    "description": "Tooltip for the dark mode switch."
   }
 }