Allows integration of GitBlit as plug-in in other projects.

There are now three new targets on the ANT build:
- buildJAR: creates a GitBlit JAR including the GitBlit biz logic
- installMaven: install GitBlit JAR as Maven module
- uploadMaven: uploads GitBlit JAR to a Maven repository

Additional extensions have been made to allow:
a) GitBlit to load his resources outside of Wicket domain
b) GitBlit to use an injected UserService
c) Generic authentication of HTTP Request using 3rd party logic
d) Load settings programmatically from an InputStream
e) Use cookie authentication OR generic HTTP Request
   authentication for Wicket pages
f) UserModel with branch-level security logic