Converted the backend model to Singleton
Switched to lazy-loading for the backend

* Loading the backend class in the backend model
* Added support for model extensions
Ensured a certain order in initializers
Minor version bump for rOCCI-core (master)
Removed trace silencers in production
Updated README, added LICENSE
Added YARD (docs)
Enabled YARD (docs)
Documented ApplicationController
Documented Model
Documented Backend