Make vnc use real yast theme (bnc #855246) and make vnc screen size configurable.

- make vnc install use proper theme
- set default vnc size to 1024x768
- support 'vncsize' boot option to set different sizes (e.g. vncsize=800x600)
- run yast in fullscreen mode so it adjusts to actual screen size
add changelog and increase version
Merge pull request #155 from yast/bnc855246

Make vnc use real yast theme (bnc #855246) and make vnc screen size conf...