This change also ties the plugin manager into the Wicket framework and
allows plugins to contribute and mount new pages which are linked by the
top navbar and repository navbar extensions.

This is the first step towards modularization and injection.  All
direct references to the GitBlit singleton within the Wicket pages
and panels have been replaced to proxy methods in the GitBlitWebApp
singleton.  There are still two Wicket classes which rely on the
GitBlit singleton; those require manual instantiation (servlet 3).

Change-Id: I0cdbbcf87959d590c446c99abb09c07c87c737bc

Change-Id: Ice5706dc0659a44f54e5bf29ca66580e3be22418

Change-Id: I9f91138b20219be6e3c4b28251487df262bff6cc

This setting originally only worked for the Summary page, but since that
page was written, other pages have offered graphing.  This setting will
now disable Google Chart requests on the Dashboard, Activity, and
Summary pages.

This is related to issue-310.

Renamed pushlog to reflog to better match it's current and future purpose.
Split PushesPanel into ReflogPanel and DigestsPanel.
Overhauled project pages and gave them a coherent purpose from the dashboard.

* Properly support timezone-based date groupings
* Polish css for the major browsers on Win & Linux
* Use Gitblit constants for refs instead of JGit constants

This is a work-in-progress and is mostly working like I want, but will require
some refactoring to make it even more useful and less complex.