a safe preview-cherry-pick of g_debugEntities from the entities branch to simplify the continuous merge process, containing a simply cvar definition

Conflicts:
	src/gamelogic/game/g_spawn.c
rename g_mover.c to g_spawn_mover.c to be more consistent with the remaining spawned entity files
rename the flow_* namespace to ctrl_* namespace and adapt the entity names accordingly
minor aesthetic string-output fixes in /entityShow
sort variables of gentity_t by similarity, so that we easier spot duplicates
rename MAX_ALIASES and MAX_TARGETS to MAX_ENTITY_ALIASES and MAX_ENTITY_TARGETS to avoid nameclashes
rename some variables for clarity
merge buildTime and startTime (when a missile was fired) into creationTime
simplify how trigger_multiple is handling spawnflags and abstract it as compat-function towards the sensors
abstract sensor_touch initialization into a shared sensor_reset function
make sensor_stage resetable and honor the negation flag, fixing behavior of unset team/stage fields in the process
make sensor_end resetable and honor the negation flag
let G_Find ignore disabled entities

this has the immediate effect of us being able to disable spawnpoints and intermissions,
but also allows us to use G_Find in other places now
enable by default with spawn and documet it related to the spawned boolean
stop searching players for spawns and intermission cams, they don't have any on them!
make sensor_stage and sensor_end notification hooks use G_Find
refactor G_Find to G_FindNextEntity
add utility function to pick a random entity from g_entities matching a specified field
minor corrections in G_PickRandomTargetFor
allow for multiple spectator and team intermission cams