Change the release system to a tag-based system

Before, releases were created by commiting a change to the manifest.json
file which updated the "version" field.

This commit changes this procedure by generating the version strings
directly in the release.bash script with the "git describe" command,
based on annotated Git tags.

Change-Id: I4de4e1040b7e9d22b4d3c8df9c0870989d966c49
diff --git a/src/manifest.json b/src/manifest.json
index 2b87baf..0b753d8 100644
--- a/src/manifest.json
+++ b/src/manifest.json
@@ -1,7 +1,8 @@
   "manifest_version": 2,
   "name": "__MSG_appName__",
-  "version": "0.8",
+  "version": "0",
+  "version_name": "dirty",
   "description": "__MSG_appDescription__",
   "icons": {
     "512": "icons/512.png",