Correct indent on logo url field
What size application image to provide hint #360
What size application image hint #360

Hint now below label and above field
Scoped css classes
Font size from px to em
Add help block
Merge branch 'devel' into feature/logo_url
Move .help-block to boostrap-overrides

This is part of bootstrap and should be here instead.
Cleanup rspec and fix old way of doing tests
Merge pull request #375 from 18F/feature/logo_url

Add help text for logo url field