healthbars are disabled when a player dies.

Place Start_Position objects on the map, players are spawned at a
randomly choosen one.

Also change push force of player prefabs to 5

This fixes players falling while dashing in the air

- prefabs need to be stored in Resources/Prefabs

Workflow:
- Window --> XmlLevelEditor

- Delete
- Click "Export..."
- Add all Scene objects as Childs to new Export-Object in Hierarchy (every Object needs to have name of prefab)
- Click "Export..." again
- new Level appears in XmlItemsToExport.xml
- copy Level to Levels.xml

- Load Level from DeserializedLevelsLoader