Code review comment for lp:~marcustomlinson/update-manager/update-manager

Alright, changes made:

- I've split the large update_snaps() function into smaller parts.
- Snap updates now occur _after_ the user has opted in to the updates.
- snapd-glib for (un)installs means just one polkit prompt now for the all snap updates.
- debs with a snap replacement that were not installed manually get marked for deletion.
- The thread is still there, sorry, though I'm not sure why it's a bad idea really.