Selection groups

[volfpeter]

Prototype for group selection handling. UI/UX is still very much up for debate (changes can potentially invalidate the underlying implementation).

Changes:

• Added a selection groups button next to the UAV status summary in the app's header. Users can create, update, delete, and select selection groups from here. This is likely a temporary location and maybe also a temporary UI.
• Selection groups are stored in the selection slice in a sorted collection (by ID). IDs are numeric and start from 1. When a new group is saved, it is assigned the first unused numeric ID.
• Selection groups have editable names. The default name is "Group {id}". There's no selection group editor UI yet (it would be a single text input somewhere), so there is no way to actually edit the group name (although the redux state supports it). A dialog felt overkill. Let's discuss this.
• I added a hotkey for selecting selection groups: g{id}. There's no hotkey yet for example for creating or updating a group (from the current selection). I'll add these features when it's confirmed we're on the right path.