wrote new cuke scenario: already generated blog

cuke scenario: generate palettes for a blog that has already had
  palettes generated for it (ie: is already in the database)

  * wrote new controller spec to test for above
  * changed palette_set model to make source attribute unique
  * updated palette_set controller #create to redirect to existing
    palette set when blog is already in database
More basic view styling
Refactored PaletteSetController spec w FactoryGirl
Refactored PaletteSet specs

* consolidated before(:each) blocks
* added fixtures for non-existent blog responses to allow
  the above
Added new tests to PaletteSetsController spec

* test that index renders correct template, and assigns correctly
* change index view to output existing palettes