Logo and Hashtag with customizer support (and HiPDI)

Logo and hashtag can be changed via customizer.
By uploading a low-res (.png) and high-res (.svg) we can achieve HiDPI (aka Retina-Display) support.

Signed-off-by: Simon Kraft <simon@krafit.de>
Change some link styling

Signed-off-by: Simon Kraft <simon@krafit.de>
Added some fancy RWD

A couple of paddings and stuff was added to make resizing possible on smaller screens

fixes #2

Signed-off-by: Simon Kraft <simon@krafit.de>