Handle tango shutter state exposed as BLISS shutter

A bliss shutter is a bit tricky.

There is not a strong API for the state. But instead this is a private state exposed by each BLISS shutter implementation.

It exists a BaseShutterState which was already handled by Daiquiri.

But it also exists a TangoShutterState with completely different states.

This MR handle both, with unittests.

BTW there is a STANDBY state which i still don't exactly know what it means. THis could be removed in the future, and replaced by one of other existing states. Like i have already do for RUNNING for example.