Remove plugin toggles from the nav drawer
This branch restores the old nav drawer layout but keeps the core changes to the transport plugins and the new ViewModel-based backend for the nav drawer. Settings for enabling/disabling each plugin are restored to the settings screen.
Plugin-related parts of the NavDrawerViewModel are factored out into a separate PluginViewModel that can be reused by whatever interface we come up with for controlling the plugins.
Most of the "new" code in this branch comes from master. I decided to add commits that revert earlier changes, rather than cherry-picking, because the changes I wanted to keep were mixed in with those I wanted to revert.