REST API: Return different errors.

Return different errors identifiers and messages in order to identify
the nature of the errors.
Remove module title from module description.

Add the title to the modal template instead.
Updated modal styles
Don't escape special chars in module titles.
Removed responsive featured h3 style
Adjust stacking context. Help menu is now under modals.
Merge pull request #809 from Automattic/nuke-title-from-description

Nuke title from description and update modal styles
Updated pot file for glotpress
Updated version to 3.1-beta1
Merge branch '3.1-branch' of https://github.com/Automattic/jetpack into 3.1-branch
make sure that readme stable tag is 3.0.2 update the contributors list