Issues with map reloading on file change

Some minor issues found when testing the new map / tileset reload feature:
- If the map reloads while you currently drag a object onto/on the map the process of addition/move is canceled. That feels a bit weird.
- The reload looses the selection in the tileset window
- Also docks like the properties dock reset their scroll position at reload

But nothing of that is a show-stopper. Only some minor weirdness.

Regards,
Ablu

Start by locating the map and tileset reload implementation in the editor and reproduce the three reported cases: dragging an object, selecting a tileset item, and scrolling the properties dock. Done means reload no longer unexpectedly cancels the drag operation or resets the tileset selection and dock scroll position.

Written by the indexing model from the issue text.