Merge branch '409-blog-fragment-in-navigation-drawer-with-tabs' into 'master'

Blog Fragment in Navigation Drawer with Tabs

This replaces the custom layouts in the navigation drawer with a
`NavigationView` and adds a menu entry for Blogs.

A Main Blogs fragment is added that holds a `TabLayout` and a
`ViewPager`. Five tabs are already added, but they just have a single
placeholder fragment that is to be replaced by the actual fragments.

Please note that the header in the navigation drawer is just provisional. I am sure @Megalox can design a better one.

![device-2016-06-02-191101](/uploads/ddffee792f67fad01158d7adc7ca904d/device-2016-06-02-191101.png)
![device-2016-06-02-191048](/uploads/a5e6def118646a02c6bcbf17e0398484/device-2016-06-02-191048.png)

Closes #409

See merge request !210