Right click/drag-select in Tileset window

Nobody has claimed this yet.

The user gets into the habit of right-clicking/drag-selecting on the map to pickup a brush. When having to go to the tileset window to get a tile or group of tiles, the tendency is to try to right click/drag, but all that does is bring up the context menu.

It would improve the workflow tremendously to keep a consistent pattern of mouse usage between the map window and the tileset window. I suggest keeping the current left mouse behavior in the tileset window and adding the same behavior for right mouse. The context menu items can be moved to a new Tileset menu on the main menu bar which could also include the "New Tileset..." and "Add External Tileset...", which are currently oddly placed on the "Map" menu.

Start by tracing mouse handling in the Tileset window and comparing it with the map window's right-click and drag-select behavior. Then inspect the main menu and current Map-menu entries for tileset context actions. Done means right-click and drag-selection work consistently in the Tileset window, with the relevant actions available from a Tileset menu.

Written by the indexing model from the issue text.