Clean up main activity layout file

I went over the XML layout file of the main activity. I have not changed
that much, just some wrap_content instead of fill_parent values for some
layout widths or layout heights. One thing I refactored was a portion of
the font style. I have created a style file for the shadow font.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>