revisit how Qt includePaths are set up

Remove code to calculate include paths from QtModule.qbs. There's no
point in doing that on every module evaluation. Instead the setup-qt
tool writes the full list of include paths to the generated module
files.

Task-number: QBS-612
Change-Id: I2919770df06dd2efcbfad4cb482b8c837de6a932
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>
beautify string template syntax

Instead of the less common syntax
    ###some key value
it's
    @some_key_value@
now.

Change-Id: Ic3b763b5d0828aaa22af6f05b55e8ede80fb47f9
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>