Wrong mapping of heating curve 2

[toggm]

Backchecking with the parameters of my luxtronik installation, the naming of the curves is confusing (IMO wrong).
Check out the changes in 4cf7cae#diff-16ab562535f7e7c38028500081d9a886af0ad00073be5161a1710a1c4b8b3956R238

Heating curve 2 points to MK1 (Mischkreis 1) but curve 3 points to MK3. MK2 is missing at all.
I suggest we clean up the naming as the curve is not really the heating curve of a MK, but of the heating itself.
Suggested naming:

Main heating curve parameters:
heating_circuit_curve1_temperature -> heating_curve_end_temperature
heating_circuit_curve2_temperature -> heating_curve_parallel_shift_temperature
heating_circuit_night_temperature -> heating_curve_night_temperature

Heating curve parameters of mixed circuit 1:
heating_circuit2_curve1_temperature -> heating_curve_circuit1_end_temperature
heating_circuit2_curve2_temperature -> heating_curve_circuit1_parallel_shift_temperature
heating_circuit2_night_temperature -> heating_curve_circuit1_night_temperature

Heating curve parameters of not existing mixed circuit 2:
heating_curve_circuit2_end_temperature
heating_curve_circuit2_parallel_shift_temperature
heating_curve_circuit2_night_temperature

Heating curve parameters of mixed circuit 3:
heating_circuit3_curve1_temperature -> heating_curve_circuit3_end_temperature
heating_circuit3_curve2_temperature -> heating_curve_circuit3_parallel_shift_temperature
heating_circuit3_night_temperature -> heating_curve_circuit3_night_temperature

@BenPru Was there a specific reason you mapped curve2 to MK3?

I would the re-naming the newly introduced sensors in my open MR as well #289

[toggm]

Adjusted namings as part of #289