set engine default to Sdl2

Always default to the best engine. If it fails,
all other supported engines are tried.
Merge pull request #4365 from hasufell/master

engine detection: fix order/redundancy
Add map beacons and radar pings
Add radar pings to BaseAttackNotifier and HarvesterAttackNotifier
Change spacebar key to move to the last visible radar ping location
Enable Obelisk charge anim and sound

Enables Obeliks charge anim and sound by using AttackTesla instead of AttackTurreted.
Match Obelisk charge anim speed with original

Without a high tick value the charge anim plays way too fast.
Merge pull request #4699 from reaperrr/patch-1

Fixes Obelisk Charge anim and sound
Fix OpenRA.Utility not being able to locate mod assemblies on Windows. Fixes #4498
Merge pull request #4702 from ScottNZ/utility

Fix OpenRA.Utility not being able to locate mod assemblies
Flood fill now treats similar grass/snow/desert tiles as the same - fixes #4695
Actors with EnableStances set to false should now ignore stance change commands.
Add upgrade rule for CrateSpawner to Utility
Update CHANGELOG
Merge pull request #4705 from Phrohdoh/DisabledStances

closes #4555
Merge pull request #4392 from cjshmyr/crates

closes #4634
Merge pull request #4704 from cjshmyr/editor

closes #4695
added an icon for the hovercraft
fixed a crash when the grenadier is sonic tank zapped
buildable hovercraft in developer mode