Bootstrap 3.0

Hello!
According to what i've written in #4806 i'm starting to work on bootstrap3 migration. It's deffinatelly not yet ready for merge but you'll see all the updates here.

Please ping me if you think something should be done in a different way.

Conversion of classes has been done by a custom shell script i've done and there are few errors in cause of that but i have that in mind so don't worry.