Spellchecking #100

This is a first version of spell checking (only works on linux and maybe mac, since i have no windows  machine available to compile hunspell as static lib). It also provides the feature to replace a misspelled word with a suggested word. The spell checking itself can be used on any QTextDocument.

I had some trouble to add a dictionary to the rcc file therefore i used a static path to "/usr/share/hunspell/en_US.aff" and "/usr/share/hunspell/en_US.dic". Furthermore I am not sure whether we should bundle some dictionaries or use the system one. The second option causes some extra work for windows clients, so I would recommend to bundle the common languages