RecyclerView support

* Implements `BaseEasyRecyclerAdapter` and `EasyRecyclerAdapter` so that now we can use easyadapter with `RecyclerViews` in the same way as `ListViews`!!
* Update target SDK and build tools to version 21
* Update demo app so now it shows two tabs, one with a `ListView` and one with a `RecyclerView` ( both using the same `ItemViewHolder` )
* Update Robotium tests and Travis Ci config. 
Do you think it's worth adding a todo here, so this doesn't get forgotten in the future?