Atlas map / PMP file compression

[elexis]

The elevation and texture arrays save in the PMP file of atlas maps do consume between 600kb and 2mb each.

72 PMP files in my scenario/ folder (including all maps in alpha23) with the total size of 95MB are compressed to 6.7MB.

Contrary to XML, the PMP file format is already binary and can't be edited by hand. There is also at most one such file loaded per match start, so it shouldn't take long to decompress in particular.