Add MainActivity with the Navigation Drawer

It is composed of a Navigation Drawer from which you can access
the most important parts of the application.

The Navigation Drawer is opened, either by sliding your finger from
right to left, or by clicking on the icon-name in the action bar.

In the future, each item will launch a new and different fragment.

Signed-off-by: AlvaroOrduna <alvaro.orduna.92@gmail.com>