Auto register static/init.js as JavaScript plugin

When plugin does not expose Guice Modules explicitly,
auto discover and register static/init.js as WebUi extension
if found by the plugin content scanner.
This simplify JavaScript development from now on
no Java (or other scripting) code/classes are
required to extend Gerrit WebUi.

(based on the idea and initial patch by Dariusz: Ia5b3cb63f62)

Change-Id: I8c793764ac1876dc62d740d28c0d4cf6b9409b10
6 files changed