Branch Management: Review Commits listing

Issues:

• commits without messages look like a display bug (Screenshot 202016-09-12 2014.35.40.png)
• the changed files label disturb the understanding of the actions
• the time stamp is heavy

Things to do:

• add a commit message when there is no message. It could be the number of files changed for example (Screenshot 2016-09-12 14.59.47.png) or "no commit message" (Screenshot 202016-09-12 2014.59.08.png)
• prevent empty commit messages altogether (NXS-4542)
• display the "N changed files" label after the commit author and date (Screenshot 2016-09-12 15.09.00)
• display the timestamp in tooltip (as github do) (Screenshot 202016-09-12 2014.59.08.png)
• Remove the "By" prefix which makes the list very repetitive (my bad) (Screenshot 2016-09-12 15.09.00)