Better imagefactory error handling

[jprovaznik]

Methods create_factory_target_image and create_factory_provider_image don't handle errors properly - there is rescue block, which re-rises an exception:
rescue => e
# TODO Add proper error handling
raise e
end

It would be better to save the error into object.errors instead of propagating the exception.

I think this is not a blocker for 2.0 release, although a user in Conductor gets only flash error message on empty page.