#63 Add screen-reader support for wxBitmapButton

[Zenju]

wxFormbuilder already allows to enter a "label" for wxBitmapButtons. Unfortunately this value is never used when generating code. For screen reader support however it is required that each button has a label.

The solution is trivial:
Just add a "SetLabel" call for code generation directly after the wxBitmapButton creation:
"newbitmapbutton->SetLabel(label);"

Regards, Zenju