Add further Danfoss specific resource items

[SwoopX]

This PR adds a few missing resource item json files:

• config/lastchange_source
• config/lastchange_time
• config/lastchange_amount

and adds a few new resource items for thermostats (primarily Danfoss specific):

• config/heatavailable -> Indicate if central heating is active. Set to true when heating period ends to prevent unnecessary valve adjustments.
• config/loadbalancing -> Thermostat runs stand alone (false) or shares load with others in the same room (true).
• config/radiatorcovered -> Radiator is standing freely (false) or is covered (true). Set this to true for Danfoss Ally to use external temp sensor.
• config/windowopendetectionenabled -> Turns the window open detection feature on or off.