CMake will set version variables itself if you give the version in the
project(), which is cleaner. Also removes some (nearly) duplicate
definitions and settings added in basic_definitions.cmake for unknown
reasons.
Removes some redundant settings (name, description, version) from the
cpack settings which already default to the values from the project()
call.
This rewrites the version info using lokid's approach of compiling it
into a .cpp file that gets generated as part of the build (*not* during
the configure stage).
Among other things, this means that changing the version no longer
invalidates ccache or cmake dependencies, and because it depends on
`.git/index` git commits will cause the version to be regenerated,
making the commit tag more reliable (currently if you rebuild without
running cmake your git commit tag doesn't update).
