Add possibility to call service lock.open on lock entity

[t-omas]

In HA lock has 3 operations - lock, unlock and open. Right now I can only lock or unlock my lock by this application but I can't open lock(unlatch= for doors that don't have handle outside).

[hatl]

For now - as a workaround - I'd suggest to use a helper entity for the unlatch.
I would need to think about how to add the 3rd option.