Augment calendar schedule period definition with entities that came to existence since its creation

[climategadgets]

Existing Behavior

Current schedule period definition is rather bland and basic, and it is parsed from a pretty simple string (schedule event summary).

At the same time, the economizer configuration can currently only be set at application startup time, with bits of its behavior even hidden in hardware configuration.

Desired Behavior

• All configurable elements of the zone behavior can be defined by a calendar entry;
• Period settings can be expressed in rich format (YAML being the primary candidate);
• Backward compatibility with the previous period definition is preserved, a WARN level log message is issued suggesting a format change upon encountering such a definition, and the verbatim text of the new period definition entry provided.

Additional Considerations

It would be helpful to implement #269 in lockstep with this one - the old format event exported in a new format would be easier to deal with.

[climategadgets]

Done as of rev. 64222de