Add global Suture.config method (and Suture.reset!)

[Justin Searls]

Let folks override configuration for the life of the process. Any options set will be forwarded to Plan and TestPlan models and stick if they're valid.

Suture.config({:database_path => "some/file.db"})

Suture.create(…) # <- will use some/file.db

Suture.reset! #<- will revert to the default