Change map extension to signal incompatibility

[garsipal]

The map version in VALHALLA has been bumped, making the maps unreadable for other Cube engines or previous versions. To signal incompatibility, change the map extension.

Proposed world extensions:
vworld/wrld/valwrld/vwrld.
The map loader would need to load both ogz files and VALHALLA maps.

It has been considered to also rename tex files to one of the following:
xtr/txtr/txr/valtex/vtex/vtx.

And script files to cbs or cscript to convey it's CubeScript files rather than pure configuration.