Support DDS files for patterns as well as png
Add the converted DDS files and start using them in the model files.
Delete all of the existing PNG files.
Merge pull request #2945 from fluffyfreak/DDS

DDS for all models
Update Changelog.txt
Forgot the new_ground station dds textures.
Merge pull request #2948 from fluffyfreak/oops_ground

Forgot the new_ground station dds textures.
Deleting old files (uppercase extension - fixin it too)
Reverting to uppercase extesions in the model file (git changes them back)
Merge pull request #2950 from nozmajner/new_ground_cleanup

New ground cleanup
Update Changelog.txt
Enable clearing of multiple assassination missions, fixes #2952
fix min/max crew contracts offer