Terrain Sets / Terrain Labels: Little Findings & Improvements

Recently I worked quite intensively with Terrain Labels / Terrain Sets and this is what I've found out plus ideas for improvements. Let me know if I have overlooked something.

1. Pattern list is not updated on Undo Labels are not updated by CTRL+Z
AsIs: When deleting a TerrainSet Label, then in the Patterns View, the corresponding Pattern is switched, which is correct. But when then hitting "Undo" via CTRL+Z, then the Label comes back, but the Pattern is still switched as the Label would not exist.

2. Keybinding for Erase Terrain
Please add the option to make the function "Erase Terrain" be assigned with a keybinding.

3. Hand Pan Tool for Tilesets
On the Map, I use the "hand pan" tool (holding SPACE) a lot to navigate. Add this function please also for the view when editing Tilesets. That would be helpful for rather big Tilesets where you are zoomed in quite close.

4. Show Grid for Tilesets
I have put "Show Grid" on keybinding CTRL+G which works totally fine in the MapView. Why doesn't it work in the Tileset View? Why can't I toggle the Grid there?

Specifications:

• OS: Windows 10
• Tiled Version v.1.8.5

Start by reproducing the four cases in the Terrain Labels, Patterns, Tileset, and Map views described in the issue, including Undo and the existing keybinding behavior. Review the relevant editor entry points and verify completion when label state restores correctly and the requested erase, pan, and grid actions work in Tileset View.