* [ufo2map] perform value checks for epairs in SetKeyValue, too

* ... by using AddEpair
* [ufo2map] directly assign the variable
* [ufo2map] initialize the ump entity string
* [ufo2map] fixed CheckEntities

* introduced in 1d44ad3e2e62738617550107c27be268c70c6b92
* fixes bug #5338 (ufo2map doesn't recognise some properties)
* tweaked some hospital sizes and backgrounds
* map [+transport] updated multiplayer support
* map [city_train] removed multiplayer support, the map is just too small
* there are only 7 alien spawnpoints in city_train map
* map [corrupter_crash] updated multiplayer support
* map [dam] updated multiplayer support
* map [england] updated multiplayer support
* adjusted the maxaliens parameter for estate map
* map [estate] removed the multiplayer support - the map is just too small
* map [ferry] updated multiplayer support
* map [fighter_crash] updated multiplayer support
* map [mine] updated multiplayer support
* map [mine] adjusted maxaliens parameter
* map [mine] added alternative entrance
* map [mine] cleanup
* removed some onClick actions from the hospital window that are no longer needed