Integrate MIT licensed Qt translations by the VirtualBox project.

* See mumble/qttranslations/LICENSE for more information.
Add back accelerator keys for Cancel in QDialogButtonBox.

* VirtualBox stripped those keys from dialogs that are universally dismissed by ESC. Without those we do
  not get matching translations for those buttons though.
Update license and build files for 3rd party Qt translations.

* Added new files to mumble_qt.qrc resource file
* Update information in mklic.pl to update license.h
* Added files to translation step in build. When using
  bundled Qt translations the define USING_BUNDLED_QT_TRANSLATIONS
  is set which is used to conditionally integrate the license
  statement.