Sort out the increasing mess coming from:
- AppContext*
- Dependencies
- Shared*
by doing the following:
- Keep in the "Shared" folder only the entities actually shared by
App/Tunnel
- Create TunnelContext
- Move AppContext and related to the App/Context folder
- Move TunnelContext and related to the Tunnel/Context folder
- Delete Shared+* extensions, use AppContext/TunnelContext singletons
from the app
- Create a Dependencies factory singleton to create entities in a single
place
- Split extensions by domain
- Make it clear with `func` vs `var` when a dependency method returns a
new instance
