Add translators to the credits dialog

- Add tooling at //tools/i18n to generate the file with the information
  about the translators: //src/json/i18n-credits.json.
- Change credits.json to remove an entry from a translator, who is now
  mentioned in the i18n credits.
- Change Makefile and release.bash to incorporate the i18n credit
  generation in the process of building the extension.
- Change options page to accommodate the translators section.

Change-Id: I7f3991f9c456c381832f4a7bebdfc5581ef9e4be
diff --git a/src/_locales/en/messages.json b/src/_locales/en/messages.json
index 3ba9d52..433fd17 100644
--- a/src/_locales/en/messages.json
+++ b/src/_locales/en/messages.json
@@ -85,6 +85,14 @@
 		"message": "by",
 		"description": "Fragment of the author statement in an item of the credits. NOTE: put in in lowercase letters. EXAMPLE: '{{options_credits_by}} Adrià Vilanova Martínez'"
+  "options_credits_translations": {
+    "message": "Translations",
+    "description": "Header for the section in the credits dialog which recognizes translators."
+  },
+  "options_credits_translations_paragraph": {
+    "message": "I would like to give a very special thank you to the following contributors, who have selflessly translated the extension interface to many languages:",
+    "description": "Paragraph in the 'Translations' section of the credits dialog, which recognizes translators. Following this paragraph there's a list with all the translators' names (if you've translated a string in Crowdin, you'll automatically be added to the list in the following extension update)."
+  },
 	"options_ok": {
 		"message": "OK",
 		"description": "OK button in the dialogs"