Track rust master + enable some default methods

Some stuff that was caught in our filter did not make it to the
default implementation in the D-Bus library.

Signed-off-by: David Henningsson <david.henningsson@canonical.com>
Interior mutability in Connection

This makes it possible to share connection references easier.

Signed-off-by: David Henningsson <david.henningsson@canonical.com>
Store connection reference inside Props

Easier API now that we can have many refs to a Connection.

Signed-off-by: David Henningsson <david.henningsson@canonical.com>
TreeMap -> BTreeMap

Signed-off-by: David Henningsson <david.henningsson@canonical.com>