Use ufo_find to reduce code duplication in the cmake find modules

[mgerhardy]

The point of this pull request is to a) use pkg-config for _nix based systems b) use built-in versions in src/libs/ automatically if not found via ufo_find (therefore the names of the ufofind lib must match the name in the src/libs dir of the external dependency) This needs more work - this pr should just prepare this. c) reduce code duplication for the Find.cmake modules

[hwoarangmy]

@mgerhardy Are you awaiting something from me ?

[mgerhardy]

@hwoarangmy no - this is just a starting point for doing some more work on the cmake build system. You are welcome to step in, but I will continue when time allows