Codechange: rework how grf and ob[msg] are generated

For grfs, it now uses CMake scripts to do its job, and both grf
files are split into their own folder to make more clear what is
going on. Additionally, it no longer builds in-source (although the
resulting grf is copied back in the source folder).

For ob[msg] it now uses CMake scripts to generate the translation
files; the result is no longer stored in-source (but in the build
folder).

Although all files are available to create the GRFs and basesets, it
won't really work till CMake is introduced (which will happen in a
few commits from here)

(svn r27730) -Change: Split openttd.grf into openttd.grf and orig_extra.grf
openttd.grf is now always loaded and provides all extra graphics in case the (possibly outdated) baseset does not.
orig_extra.grf contains graphics specific to the original baseset only.