This fixes #1059

It would be useful to be able to push a complete repository with a
refs/gitblit/tickets branch and have Gitblit index all those tickets.
Additionally, it would be nice for the mirroring service to recognize
an incoming update to this ref and fire an event that can be processed
by the BranchTicketService, if so configured, to reindex the tickets.

Change-Id: I5f0f50f4ae7d332e9f724a2e6f074fa71f646035

Change-Id: I9bb2cc0cbfac9841b13bed15a474fefb24355cd4

These manager interfaces define how the GitBlit singleton will
eventually be split into smaller component managers.  The Wicket app and
all servlets have been updated to request the needed managers.  There
are _very_ few method signature changes - although there are a handful.

This is a surgical sharding of responsibility based on a proof of
concept refactor.  Instead of random references to  GittBlit.self()
there are now precise references to the manager interface required to
accomplish some task.  Some tasks may require references to multiple
managers.

The code is now littered with calls to GitBlit.getManager(class) and
those familiar with the code-base will no doubt notice the duplication
of methods from IUserService in IUserManager and the addition of
implementation methods in the GitBlit context class.  When the
GitBlit class is broken apart and the existing external authentication
user service classes are refactored to AuthenticationService classes,
this will again simplify and flatten.  But in order to safely and
cleanly modularize the stable code-base we will have to live with a
little duplication for a short while.

Change-Id: I7314ec8acaab2dcc6092785ed4434cc09fdbbe16

The mirror executor will fetch ref updates for repository mirrors.  This
feature is disabled by default and can be enabled by setting
git.enableMirroring=true.  The period between update checks is
configurable, but it is global.  An individual rpeository may not set
it's own update schedule.

Requirements:
1. you must manually clone the repository using native git
   git clone --mirror git://somewhere.com/myrepo.git
2. the "origin" remote must be the mirror source
3. the "origin" repository must be accessible without authentication OR
   the credentials must be embedded in the origin url (not recommended)

Notes:
1. "origin" SSH urls are untested and not likely to work
2. mirrors cloned while Gitblit is running are likely to require
   clearing the gitblit cache (link on the repositories page of an
   administrator account)
3. Gitblit will automatically repair any invalid fetch refspecs with a
   "//" sequence.

Change-Id: I4bbe3fb2df106366ae4c2313596d0fab0dfcac46