Removed music-old
Removed mission 101
Revert "Removed mission 101"

This reverts commit 13cf10a4fa559dabb485f9e9607243f3e41622d0.
Replaced reliefs 41 & 47 with ones from original game

Issue colobot/#299
Show warning if po4a is not installed
Updated author.txt and splash screen
Updated generic help files
Removed unused Russian translations files

These are copies of files in "bots" category
Fixed filenames in Polish translations
Made music a submodule