Preset functionality (Holiday function, Removal of surplus heat)

[sbv1307]

Add functionality which by one command, can set an individual presat low temperatur i every room

[sbv1307]

Merged #7 into this issue, because the solution will be the same. Solution:

• Define a structure, which will hold the setpoint temperature for each thermostat. The structure shall handle setpoints for "Normal operationmode", "Holyday operationmode" and "Surplus heat operationmode".
• An element in the structure for the given operation, will be updated, when ever the setpoint is read from the thermostat, and has a new value.
• When an operationmode changes, setpoints the current operationmode will be saved to memory, and the setpoints for new operationmode will be read from memory and the thermostats will be updated.