Improved badges
Updated contribution guide
Merge pull request #4334 from GrahamCampbell/4.1-badges

[4.1] Improved Badges
Merge pull request #4367 from GrahamCampbell/4.1-contr

Updated Contribution Guide
Merge branch '4.1'
Upgrade stability on 4.2 branch.
Upgrade branch alias on master branch.
This doesn't need to change.
Merge branch '4.2'
Update version on master.
Add collection item attribute average