Too much for one release

Loads of stuff happened this release, so we're bumping version to 0.8.0.
Note as well that there is a small change to tabsarray type regarding its title, the title is now
interpolated instead of eval'd. So if you have any problems slap on a {{ }} around the tab title.
See the docs on tabarray for an more info.

• Custom validation via ngModel.$validators and ngModel.$asyncValidators, thanks @davidlgj
• Inject errors from backend directly to a field with events, thanks @davidlgj, @burdiuz, @jdgblinq
• Icons to button type, thanks @maff
• Fixed spoiled comment, thanks @mchapman
• A new template field type, insert a angular template, like a mini add-on.
• Support for schema type that allows null, thanks @ulion
• Option groups in selects, thanks @DennisHalmstad
• input group addons, thanks @quietlyconfident
• validationMessages overhaul, nicer validationMessages with interpolation and a new sf-messages
  directive for add-on to use. thanks @davidlgj
• interpolation instead of eval'ing in tabarray title, thanks @Coridyn
• Lots of bugfixes, most notable checkboxes validation now works, thanks @davidlgj, @Coridyn,
  @ulion, @adamcbuckley