Add state machine

[spacemanspiff2007]

Add a simple state machine that plays nice with the HABApp environment.
Make it so the users can add building blocks for automatic state transition (e.g. transition if item > 5) to make usage easier.
I'm torn between making the state machine an HABApp internal item or a helper class that will be assigned as a rule variable.
In both it should be able to automatically push the current state to an openHAB item.
If it's stand alone it could be configured e.g. from some kind of yaml?

@nobbi1991
You're using a couple of state machines in your rules and I'd like and value your input on this.
How do you use your state machines and what features would you expect from an HABApp implementation?

[Rosi2143]

Hi @spacemanspiff2007,

I made very good experiences with python-statemachine. It has a lot of great features and I added it into many of my rules.

How about adding this module as a dependency - I just added it to the list of packages in my installation and it works like a charm.

[nobbi1991]

I use https://github.com/pytransitions/transitions, since it also supports hierarchical FSMs.
From my side no additions to HABApp are needed.

[spacemanspiff2007]

I thought it would be nice to have an item (HABApp internal order openHAB item) which reflects the current state the item is in.
Sending commands to the item could then trigger the corresponding transition to the next state.
I looked a little bit at python-statemachine but it keeps an internal reference to the event loop which breaks things during testing. Transistions does only allow sync or async callbacks but as far as I saw not a mixture of both.
It's also always difficult if the library launches it's own threads/tasks because we don't get the nice HABApp tracebacks and cleanup on rule reload is often not possible.