`gui/siegemanager` Further improvements to UI

[amade-w]

I think there's still value for gui/siegemanager compared to the native feature as it has keyboard shortcuts for all the actions.
Additionally, you can open it with one keyboard shortcut (if you make one for it), compared to the native feature which requires either 2 clicks or 1 shortcut + click to open.

Suggestion: add a custom clickable icon (like the general search button or the mass removal interface) to bring up the gui and place it next to the squad button. Also add a keyboard shortcut to open it so users don't have to do it themselves (I'd recommend avoiding combinations using S, because I just accidentally saved my game while trying out shortcuts without refering to dfhack.keybindings.init).

Suggestion 2: make the 'Configure All' setting also affect clicks, i.e. similar to how the top row works in the native feature.