Template system modifications + PoloniexNight theme

- Default theme is now explicitely declared as directory (hardcoded styles
from *.cpp are moved there)
- $theme-dir var points to current theme ($themes-dir still points to
  themes main directory)
- More things styled (e.g. ComboBoxes, Nofiticator window in Linux, and
  many more)
- vars in vars are not allowed now (problems with order)
- PoloniexNight theme added
Merge remote-tracking branch 'upstream/master'
Themes screenshots
Merge pull request #16 from zeewolfik/master

PoloniexNight theme + hardcode styles (not all) removal + coincontrol dialog timezone fix