Internationnalization: buggles etc.

Coded in the i18n.tr calls.
Put the base support as much as possible into the abstract classes. the
derived classes only having to add registration code and language
selection handling (see World, BuggleWorld and
EntityControlPanel/BuggleButtonControlPanel).
Todo: build the .pot/.po files
Merge pull request #96 from fstengel/Test

Internationnalization: buggles etc.