SAT integration improvements

[oliof]

The current beta implementation of SAT works to some extent, for example on boilers that speak EMS(plus) but don´t have a thermostat like the RC3*0 or a (dummy) remote thermostat installed. With those boilers in the mix, there is room for error:

• it's not clear what control mode an existing boiler thermostat should be configured to
• It's easily possible to get into a mode where the boiler control and SAT control start overwriting each other, killing all possible efficiency gains.

To ensure that SAT actually has control over the boiler, it should be integrated like a remote thermostat so that the boiler expects control from that.

There may still be some control gaps -- in my case for example the boiler ignored force heating off and a low burner power setting, which usually is enough to disable the boiler. My assumption is that either the thermostat setting, or the outside temperature input, cause the RC310 on my boiler to ignore/override the commands SAT sends.

In addition, there needs to be more documentation about

• control mode the boiler should be set to.
• how to ensure that SAT sending commands to the boiler stays authoritative.

[oliof]

#2257 (comment) describes how OTGW handles thermostatic control

[oliof]

Another note: While my setup seems to ignore/override the force heating off override, it can reliably be turned off and on by toggling the boiler/heatingactivated/ setting. EMSESP documentation points out that heatingactivated is not settable on all EMS capable devices, so we may need to have a way to detect how to reliably switch of heating, or a static mapping from boilers and versions to commands.