Better/more granual Temperature Hysterese Handling

[rudiratlos]

pls. make the tolerance value more granular, like generic thermostat is using:
cold_tolerance: 0.75 # same function as tolerance value
hot_tolerance: 0.3 # this is an additional/new value
pls. allow, that both values can have negative values also
function description:
heating on: current_temp - cold_tolerance < desired temp
heating off: current_temp + hot_tolerance > desired temp

reason:
I have a very sluggish underfloor water heating/cooling.
Using tolerance value only, the heating is overshooting by 1-2 degrees.
By setting hot_tolerance value to -1.5, overshooting can be prevented.

[KartoffelToby]

#1436