Get rid of Method B to create and bind ViewHolders

[davideas]

Method B is the classic way to implement the Adapter by overriding onCreateViewHolder() & onBindViewHolder(). Those methods will be now declared final because Method A will be the new standard.

From now on, we will use only Method A: we will delegate the previous operations to the item interfaces.
Item interfaces will now mandatory implement the following methods:

• getLayoutRes()
• createViewHolder()
• bindViewHolder()