Multi-language support and Settings window (with language settings) added

This adds a new Settings window where you can choose the interface language. The language setting gets loaded and saved in the new "settings" table in the database.

The TRANSLATIONS_DIRECOTRY in translation.h defines where the translation files (.qm) are. I've set this to "translations", so you have to add a folder named "translations" in your build directory  and copy the .qm files to this folder.

I have added a German translation, but I've translated only 2 windows (Settings and Deposit) as there probably happen a few changes in the UI until the first release.

For more information on how to add new translations, generate new template-files for translators and make them ready for realease see the /documentation/translating file.