Add api to delete logical switch and bindings

Also set BigInteger instead of Integer in the Physical_Port and
Logical_Switch sets, to avoid cast exceptions with Integer despite
declared types.

Adding also a small test class useful for manual testing.

Change-Id: I6bc104b43e276179e18a65742c2497b41e693c17
Signed-off-by: Galo Navarro <galo@midokura.com>