Implement contribution statistics: https://bugzilla.redhat.com/show_bug.cgi?id=1092193

Squashed commit of the following:

commit 47aa02d4b3aca64775a202e1366cd95993e9a2b4
Author: Alex Eng <aeng@redhat.com>
Date:   Fri Oct 24 11:26:30 2014 +1000

    Refactor, add comments on contribution statistic implementation

commit af0b47198a2cd077aa3a6fa4fc7ee248ef28ede3
Merge: 122c7d8 d2d8e22
Author: Alex Eng <aeng@redhat.com>
Date:   Wed Oct 22 15:52:29 2014 +1000

    Merge branch 'integration/master' into rhbz1092193

commit 122c7d863336832f432810968b09a81c413389b0
Author: Alex Eng <aeng@redhat.com>
Date:   Tue Oct 14 13:18:53 2014 +1000

    Unit test for contribution stats

commit 83b9364a6f5e502321e7dcab7d8c7a579cca44d0
Author: Alex Eng <aeng@redhat.com>
Date:   Fri Oct 10 15:43:32 2014 +1000

    Create query for contribution statistic

commit d750548e79eebbffd07e8ba4d63202d105823045
Author: Alex Eng <aeng@redhat.com>
Date:   Thu Oct 9 14:16:32 2014 +1000

    Create rest endpoint for contribution statistics
Fix loading on webook, add message when removing webhook
Merge branch 'integration/master' into rhbz1122776

Conflicts:
	zanata-war/src/main/java/org/zanata/util/StatisticsUtil.java
Refactor org.zanata.ui.model.statistic to org.zanata.model.statistic, change webhook event to translated+approved and approved
Merge branch 'rhbz1122776' of github.com:zanata/zanata-server into rhbz1122776