Move template to designated cmake/ directory
Pick up description from one place
Don't hardcode the library name in templates
Make template instantiatable for multiple projects

The name "opm-project" is replaced by the real name of the project.
Move now generic templates into cmake/ directory

Templates can now be reused across projects. The output files are still
put in the root of the output tree because that is where the client
programs will look for them.
Move stylesheets into Documentation/ folder

The Doxyfile is still in the root directory because this is more like
a configuration file, and also its presence will be a cue to some
users that Doxygen is possible to run on the project.