Toolbar UI buttons to show/hide/modify designation priorities

[Bumber64]

Add UI buttons to the designation "Show advanced options" toolbar, in the style of dig.warmdamptoolbar.

The first button should affect game.main_interface.designation.show_priorities, which is responsible for showing priority numbers on all designated tiles (when in designation mode). In vanilla DF, this is set to true when clicking any priority setting, and only set to false when quitting to main menu (or restarting DF). There's no persistence between game sessions, and no convenient way to hide them again within a session.

This button should persist the true state between sessions, and can toggle off display of priorities manually. We could have an option to automatically revert show_priorities to false state if only priority 4 designations remain on the map, but that means keeping track of the state of all non-4 designations. We may also want to force priorities to be rendered outside of designation mode (for use with gui/design, etc.), which we'd probably have to do manually.

The second button should allow modifying the priority level of designations within a box, current z-level, or entire map without modifying the designation type. This works similarly to DF's blueprint marking buttons. The z-level or map options are located inside the tooltip like with dig.warmdamptoolbar. Priority of valid affected tiles is set to the currently selected value of game.main_interface.designation.priority. We could have an option to only target a selected range of priority levels for modification.

There is space for these buttons to be located on either side of the priority number options (though it might look crowded). The priority options move around for various designation modes, so the UI state will have to be checked for various cases.

[Bumber64]

The second button could just be a part of gui/design instead, but that would make rendering priorities outside of designation mode mandatory. It would also likely be expected to stop rendering them when the gui/design window closes, unless we add the option to the first button in addition.