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/injections/ccdarktheme_switch.css b/src/injections/ccdarktheme_switch.css
new file mode 100644
index 0000000..c0d94f5
--- /dev/null
+++ b/src/injections/ccdarktheme_switch.css
@@ -0,0 +1,8 @@
+.TWPT-dark-theme {
+  padding: 4px 8px;
+  cursor: pointer;
+}
+
+.TWPT-dark-theme .content {
+  padding: 8px;
+}