Improve status message on merge request page

The status message currently looks like:

  Created on Oct 24, 2013 by John , currently assigned to Bob

There is a space between the author name and the comma, which is
incorrect.  Also, there is no period at the end of the sentence,
which makes it inconsistent with the following line:

  Merged by Bob 5 minutes ago.

Change it to:

  Created on Oct 24, 2013 by John.  Currently assigned to Bob.

Also change the milestone information from:

  and attached to milestone XYZ

to:

  Attached to milestone XYZ.
Merge pull request #5557 from dpursehouse/merge-status-message-improvement

Improve status message on merge request page