lib/ur brings in a lot of dependencies we don't need in e.g.
stcrashreceiver, who only needs the small failure reporting structs.
Make those part of the lean `contract` package instead.
Signed-off-by: Jakob Borg <jakob@kastelo.net>
Move infrastructure related commands to under `cmd/infra` and
development stuff to `cmd/dev`. The default build command builds the
regular user facing binaries: syncthing, stdiscosrv, and strelaysrv.