+ things as sprites on map, controlled with am_showthingsprites CVAR

drawing of sprites instead of things/players markers with am_cheat >= 2
possible am_showthingsprites values are:
0 - sprites disabled
1 - static front sprites
2 - animated front sprites
3 - animated sprites with actual things angles
Merge branch 'map_sprites' of https://github.com/alexey-lysiuk/gzdoom
- fixed sprite rotation in automap submission
- added menu option for sprite display on automap.