Added branch and tag identifiers to log history

Added branch and tag labels to the log history. Previously, the user had to right-click the log and select "Branches" or "Tags" to view the available branch and tag history. This update now displays the branch and tag names next to their associated check-in. This update also centers the username/password dialog when prompting for auth.

Branches are bold.
Tags are italic.

![Branches and tags displayed in log history](http://i.imgur.com/GSv8Od8.png)