Drop translations from source levels

- *.{F,D,P} are dropped from the source
Don't alter source levels anymore

- Build them in another directory.
- That "other" directory is the cmake binary dir.
Minor: numbered status updates in generation script
Minor: Rename some confusing variable names
Simplify gen_levels_xml for increased resistance
More cleanup

- Drop *-po4a.cfg files (which are useful for build-time only),
- Add more exclusions to gitignore.
Rewrite CMake levels installation
Merge pull request #4 from OdyX/dev-update-levels-i18n

Rewrite the levels' i18n handling