Add "Force Mark as Read" feature

This change adds a feature to the extension which will mark all threads
as open when visiting them from the Community Console.

This works by making a request to load the thread again (so the
extension knows the last message ID) and then making a request to mark
the thread manually as read, passing the last message ID so the
Community Console knows that's the last message we've read. This last
request is the one which is made when manually marking a thread as read
from the thread list.

This change also adds the file api.js with a wrapper function to call
the Community Console API. In the future, all API calls should use this

Change-Id: Iff1c077bf136807cdbaa710e2e6b8b130df3a27e
diff --git a/templates/manifest.gjson b/templates/manifest.gjson
index 2a7c440..67eeab6 100644
--- a/templates/manifest.gjson
+++ b/templates/manifest.gjson
@@ -18,7 +18,7 @@
   "content_scripts": [
       "matches": ["*"],
-      "js": ["common/content_scripts.js", "content_scripts/console_inject.js"]
+      "js": ["common/api.js", "common/content_scripts.js", "content_scripts/console_inject.js"]
       "matches": ["*"],