Previously the cmake boolean switch QTONLY was used to build
bin/marble as a KDE application (QTONLY=FALSE, default) or as
a Qt application (QTONLY=TRUE, no KDE dependencies at all). This
approach has some drawbacks:
- it's not immediately clear which version (KDE or Qt) bin/marble is
- you cannot build the KDE and Qt version in one go

Having bin/marble and bin/marble-qt separated fixes that:
- bin/marble-qt is the Qt version, always there.
  bin/marble is the KDE version
- bin/marble and bin/marble-qt are both installed at the same time
  (great for testing and for distributions for packaging)

Warning: For continuous builds with QTONLY=TRUE, please delete bin/marble
now. Execute bin/marble-qt in the future.

Note: Tested with QTONLY=TRUE/FALSE, but only on Linux. Please report
any breakage you might encounter.

Further reduction of QTONLY usage in cmake files should come in
future commits. The CMAKE_INSTALL_PREFIX subfolder structure might
change as well.

CCMAIL: marble-devel@kde.org