Fixed Doxygit.cmake for 'make doxygit', added CommonDocumentation.cmake.

Right, but in our case it has the drawback that the DOXYGIT_TOC_POST and DOXYGIT_MAX_VERSIONS have to be specified in every project, or read again somehow from a file configured during the intialization of the documentation project. All of this requires extra engineering effort to work correctly for almost no benefit (see my other comment above). I feel that we need to avoid creating overly complex tools and I so vote for simplified verision here. But if you disagree, we can revive the previous pull request and merge it.