Github status comment

This will add initial support for a status comment on GitHub than might hold information from issues.joomla.org not present on GitHub.

Currently only user test results are displayed, since this seems to be high priority.

Since this is a new feature, status comments for existing issues will be created at the **end** of the comment list and only if the PR gets updated.

Example: https://github.com/jtester/tests/pull/44#issuecomment-58175648

Ref #510, #511 
Fix #519