Improve version.pri to set a version number only in one place.

Now you can set values like VER_MAJOR, VER_MINOR and so on, and PROJECT_VERSION will be built based on them.
If I am interpreting this correcly a version of VER_MAJOR=3, VER_MINOR=2, VER_BUILD=0 will appear as "3.2" and not "3.2.0", right?
I don't want this. At least 3 numbers should be visible.