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Don't run SimpleCov on Travis

Show only the commits that are newer in the merge request.

Allow disabling Gravatars in gitlab.yml settings

2. SSH Keys Help page

Speed up the "Project Network Graph" cucumber feature

This change involves stubbing out the call to `Grit::Commit.find_all`
and limiting the number of commits to 10 vs. the standard of 650 used by
`Gitlab::GraphCommit.to_graph`.

Prior to this change, this single feature required almost 3 minutes of
running time and over 2 GB of memory on my machine. Now it takes less
than 3 seconds.

Conflicts:
	app/models/user.rb