[Issue 515] Added user customization of digits grouping space size.

https://code.google.com/p/speedcrunch/issues/detail?id=515

Basically, the patch changes Settings::digitGrouping from bool to int, its value being the number of spaces to use to separate the digits groups (from 0 to 3, 1 was previous default). There's no compatibility issue with the content of previous version settings files as bool can be converted transparently to int by QSettings.

Translations, '&' menu keys and hotkeys are missing.