Fix for issue #890

Modified the potential_mentor_count to return the number of mentors in
the project. Also, changed the test and made the result.html to work as
paulproteus has suggested. Should the function be renamed to
get_mentor_count ?
Update tests.py
1. len() has been replaced with count()
2. Number of mentors will only be printed if there is atleast one mentor
in the language
Update result.html
Replace twill tests with django-webtest in profile tests

Also, remove un-used Starlings unit test and a test that
references a non-existent website url.
1. Rename potential_mentor_count to mentor_count - Done
2. "Mentors: 0 and 0 in Objective C"? - This will not be printed. The
condition has been changed to check that the mentor count will only be
printed if the project has mentors.
3. Remove the use of the values_list - Done. We now only call count on
the people in the tag query.
Fix issue1448 - Actually fetch the blog
Updated GitHub URL regex. 

GitHub project names are allowed to have dots in them. https://github.com/gratipay/gratipay.com for example.
Merge pull request #1439 from onceuponatimeforever/1343

Replace twill tests with django-webtest in profile tests
Merge pull request #1453 from Deborah-Digges/issue1448

Fix issue1448 - Actually fetch the blog
Merge pull request #1431 from moijes12/890patch

Fix for issue #890
Merge pull request #1457 from rohitpaulk/patch-1

Updated GitHub URL regex.