commands: move activebookmarklabel to bookmarks module This is going to be used in an upcoming patch that moves more methods to bookmarks.py.

commands: replace locking code with a context manager Note that this means that we're unnecessarily creating a transaction in the pure "--inactive" (i.e. when deactivating the current bookmark), but that should be harmless.

bookmarks: factor out adding a list of bookmarks logic from commands We keep the lock in the caller so that future devs are aware of the locking implications.