Add additional capabilities for specifying entities with target time

[alinbalutoiu]

This PR adds additional capabilities to highlight target times:

• It makes the background color customizable
• It allows you to set a prefix for the date (useful if you want to add emojis for example)
• It makes possible to add as many target times as you want

It does also mean it's breaking previous configurations since targetTimesEntity and targetTimesEntity2 is no longer supported.

The migration is pretty straightforwad, from:

targetTimesEntity: binary_sensor.octopus_energy_target_rate3
targetTimesEntity2: binary_sensor.octopus_energy_target_rate4

to:

targetTimesEntities:
  binary_sensor.octopus_energy_target_rate3:
  binary_sensor.octopus_energy_target_rate4:

Finally, here's a picture on how that looks like.

Addresses the following:

• Fixes #64
• Fixes #57

[corvus2606]

good solution, better than mine 👍

[lozzd]

This is very nice!

One minor thing, your example config section (and great screenshots on this PR for that matter) - could you move that in to/replace the content under the "advanced configurations" section further down in the README?

I'll need to write up a note about the breaking change for the release notes but that's fine.

[alinbalutoiu]

I've updated the README, let me know if that works.

I had a separate text card in home assistant which was showing the target time intervals, but this is making life so much easier, thanks for adding support for it initially!

[lozzd]

Thanks very much! love the feature. This is now released in v0.6.0 with the note about the breaking change in configuration format.