Localization

Some files. Last commit before refactoring of localization methods.
Localization

Performed changes to the engine:
MainFrame now implements currentHumanLanguageHasChanged and changes
(some for now: buttons) UI elements within.

Eventually all UI classes will use this mechanism…

Added an english localization...
Localize MainFrame: using currentHumanLanguageHasChanged

There might still be some work to do. Especially one could devise a
series of helper classes to handle UI items uniformly.
Merge pull request #88 from fstengel/master

[UI] work on localization.