Manually reset/clear undo/redo command stack

[gajop]

Display history of executed commands
Have it support multiplayer (cooperative) work

[gajop]

Create a manual button for clearing the undo/redo stack or do it automatically:
https://springrts.com/phpbb/viewtopic.php?f=85&t=32544&p=568269#p568259

[gajop]

4fe767a