[P027] Add optional Powerdown mode

[tonhuisman]

Resolves #2248 Resolves #3481

Features:

• P027 Add Powerdown mode (optional) to reduce the quiescent current when not taking measurements, f.e. during sleep mode in battery operated configurations.
  • This feature is not available in LIMIT_BUILD_SIZE builds (Display, Collection, Climate) for bin size reasons.
• Extend/Update documentation.
• P027 Fix sending single values via Controller as reported in #3481

TODO:

• [ ] Testing
• [ ] Update documentation