Building extension files

Adds possibility to build extension files (Chrome and Safari) from
command line.

To run from the project directory:
python tools/build.py [meta]

If the optional `meta` argument is set, then only the manifest and
language files are uptated.
Without that everything is being built (extension files too) into the
`dist/build/version_number` folder.

For Chrome there will be two files, a crx, and a .zip file which
includes the key.pem private key (so this must not be shared,
it's just a bit help for publishing it to the Chrome Web Store).

Beside the extension files, update-files are generated too (for self
hosting - Safari needs it).

src/js/vapi-common.js

@@ -1,3 +1,4 @@
+// » header
 // could be used for background and other extension pages
 
 (function() {
@@ -37,8 +38,10 @@ vAPI.download = function(details) {
         messager.close();
     }
 };
+// «
 
 if (self.chrome) {
+    // » crx
     var chrome = self.chrome;
 
     vAPI.getURL = function(path) {
@@ -50,7 +53,9 @@ if (self.chrome) {
     };
 
     setScriptDirection(vAPI.i18n('@@ui_locale'));
+    // «
 } else if (self.safari) {
+    // » safariextz
     vAPI.getURL = function(path) {
         return safari.extension.baseURI + path;
     };
@@ -119,6 +124,8 @@ if (self.chrome) {
             }
         });
     }
+    // «
 }
-
+// » footer
 })();
+// «