Rename gem to hydra-curation_concerns and update namespaces accordingly

[flyingzumwalt]

• rename the gem from worthwhile to hydra-curation-concerns
• replace CurationConcern:: namespace with CurationConcerns:: namespace (plural instead of singular)
• move everything from Worthwhile:: namespace into CurationConcerns:: namespace and move/rename files/directories accordingly (ie. rename worthwhile-models to curation_concerns-models)

Update code & tests as necessary.

Then Rename github repository from worthwhile to hydra-curation_concerns (ticket #40).

Note: I don't think you should put everything inside of the Hydra namespace. I think it's safe to put the CurationConcerns namespace at the top level of the Object space (ie. CurationConcerns::WorkBehaviors instead of Hydra::CurationConcerns::WorkBehaviors) but include hydra in the gem name and the repository name (hydra-curation_concerns) for clarity of ownership & domain of relevance. I would also be ok with leaving hydra off of the gem name and repository name. It's not like people are going to come across a gem called curation_concerns and be like "But which curation_concerns gem is this? Is it the Hydra one or the one from Twitter?"

See Code Shredding doc for a guide