CMake: Move biblio test projects into tests group
CMake: Add target update-gmo

This target will update the gmo files if and only if the associated
po-file is modified. To determine whether a file is modified, 'git
status --porcelain' is used.

This follows up on commit 06782542.
CMake: Put the docs projects in a subdirectory
CMake: Regenerate deleted gmo files
Style