return API exceptions as JSON

[bmesuere]

Original issue by @bmesuere on Fri Aug 22 2014 at 14:52.

[bmesuere]

this needs more thought:

• when in develop mode, html exceptions are fine
• when in production mode, error mails with all info + short response are needed

Each error needs to be specified separately: http://guides.rubyonrails.org/v2.3.11/action_controller_overview.html#rescue

Original comment by @bmesuere on Wed Aug 27 2014 at 14:11.