GadgetBorrowPanel is now displayed correctly and allows filtering.
UserMasterPanel is the counterpart to the UserDetailPanel, which is now
simply used upon GadgetBorrowPanel as control.

GadgetDetailFrame is now listening to ENTER- and ESCAPE-KeyPresses like
it was demanded.

Lots of minor fixes including äöü-Errors also implemented.

Code to  prevent the user from opening multiple frames of the same kind
was only added as comment because it is not working...