and issue a proper error message if not.
When using linuxdeployqt for example in OBS and packages can not
be installed, it can happen that the desktop file is not existing.
This error message makes debugging easier.
Refactor the project structure to make it build as a "Qt module". It's a first step to get this tool closer to Qt.
The main advantage here is: Simply running:
```
qmake
make
make install
```
will compile and install the tool into your Qt installation, and make it a part of your Qt just like any other tool (qmake, etc.)