Prepare for 2.7.0 release

[elihart]

• New If a @ModelView generated model has a custom base class the generated model will now inherit constructors from the base class (Make generated models from views inherit constructors from base model #315)

• New Use the EpoxyDataBindingPattern annotation to specify a naming pattern for databinding layouts. This removes the need to declare every databinding layout explicitly (Wiki - Databinding naming pattern support #319)

• New If a view with @ModelView implements an interface then the generated model will implement a similar interface, enabling polymorphism with models. Wiki

• Improvement PagingEpoxyController now has getters to access the underlying data lists (Thanks to @pcqpcq - add support for get currently being displayed data #317)

• Improvement EpoxyModelGroup now supports partial rebinds (Optimize model group partial binding #316)