Expose MergeRequest object as a notable in the API to allow for easy ret...

Displaying commit on a new window, when clicking commit on network graph.

Improve overlap of lines in network graph

Switchable the main branch on network graph

Fixed a grammar mistake in alert-message.block-message

Fix #2790

remove incorrect information about the api version

The API version is currently not equal to the gitlab major version number. Gitlab 4.1 
still uses API version 3. Point to the lib/api.rb file instead which contains the
autoritative information.