Merge branch 'dev' into dev-physfs

Temporarily reverted level structure changes because of all the conflicts
Reorganized level files (again)

This time also moved some help files around
Loading all mods found in "mods" directory
First part of rewriting scripts for level translations

 * support translating the new chaptertitle.txt files
 * handle the new directory structure
 * move writing PO4A config to CMake
 * use only one bash script to generate translated files
 * additional step of cleaning *.po and *.pot files
 * change some PO4A flags for better console output and sorting of
   messages in *.po files
Better fix for message ordering issue
Align chapter title translations

 * align files to new format
 * add missing translations
Remove code prefix from translations
Rewrite level files translations
PO4A: don't break messages across lines in *.po files
Align level translations
Remove unused po files
Finish rewriting translation generation: help directory support
Align help translations
Nicer generated directory structure
Align po files after refactoring
Fix installation of chaptertitle files without PO4A