Fixes issue #691

This fixes the encoding issues around datetime formatting. It introduces a new module l10n that aims to make localization a little easier. If the language and/or encoding can not be determined it defaults to en_US and ISO8859-1. The use of ISO8859-1 prevents decoding errors, but may result in foreign or wrong characters being displayed when locale formatting options are used.
At the moment it offers formatTimestamp and getTranslationLanguage functions:
formatTimestamp returns the provided timestamp (or current time if ommitted or the wrong type) as unicode (default) or raw bytestring. 
getTranslationLanguage simply returns the users language. It is the result of refactoring the QtTranslator initialization for the Qt GUI.