Qt SCXML: Unite component XML: SCXML and Core: State Machine

After merging both into one module, the decision was taken to still offer two independent modules to the world. this affects the documentation, the installer point of view and of course the build system view.

Unfortunately the two moduyles are still part of the qtscxml.git repo. It would be much nicer to have a statesmachine.git repo. It would require the need for the temporary hack on the installer side too. Ideally we want to rename the git repo but this might break certain development setups or the CI. Maybe we can achieve this via alias system on gerrit. As part of this task it shall be investigated whether we can rename/alias the repo and if possible take the necessary actions..