Implemented report of blueprint activity

* Introduced report that shows blueprint details followed by list
of commits, emails and reviews related to that blueprint
* Mail body is stored in runtime storage
* External links are opened in new window/tab

Implements blueprint report-blueprint-activity

Change-Id: I1515d7fc51a4b46932fc15551c94f0fa6b16e4ed
Merge "Implemented report of blueprint activity"