Feature: "Number" domain

[micw]

Hello,

I'm using and loving this piece of software. Recently I changed my garden water entities from light to number because that fits way better. Would you mind to add support for this domain?

Proposal:

• The action is "set value"
• "unit_of_measurement" should be used from the entity to display the unit
• "device_class" could be used to show an appropriate icon

[arthurdent75]

The main working principle is to work on entities that support _turnon and _turnoff services.