Bump rails to 4.1.2

Also update the rest of the gems to their
latest versions
Add spring binstubs
Add byebug gem for debugging
Change `Post#tag_names=` in order to work with

both tags separated with commas and no spaces after and
tags separated with commas *and* spaces after.
Do not allow users to like the same post more than

once
Merge pull request #1 from Agis-/master

Update gems and add spring binstubs