Update add-on description, make strings localisable, add German localisation

Makefile

@@ -1,5 +1,6 @@
 FILES := manifest.json \
          video-bg-play-content.js \
+         $(wildcard _locales/*/messages.json) \
          README.md
 
 video-bg-play.zip: $(FILES) Makefile

_locales/de/messages.json

@@ -0,0 +1,11 @@
+{
+  "extensionName": {
+    "message": "Videowiedergabe im Hintergrund",
+    "description": "Name der Erweiterung."
+  },
+
+  "extensionDescription": {
+    "message": "Spiele Videos im Hintergrund ab, auch wenn eine Seite dies nicht möchte.",
+    "description": "Beschreibung der Erweiterung."
+  }
+}

_locales/en/messages.json

@@ -0,0 +1,11 @@
+{
+  "extensionName": {
+    "message": "Video Background Play Fix",
+    "description": "Name of the extension."
+  },
+
+  "extensionDescription": {
+    "message": "Play back videos in background even if a page doesn't want you to.",
+    "description": "Description of the extension."
+  }
+}

manifest.json

@@ -1,9 +1,10 @@
 {
   "manifest_version": 2,
-  "name": "Video Background Play Fix",
+  "name": "__MSG_extensionName__",
+  "default_locale": "en",
   "version": "1.3",
 
-  "description": "Some sites may not work with Firefox video background play feature. This add-on provides a quick fix.",
+  "description": "__MSG_extensionDescription__",
 
   "applications": {
     "gecko": {