Thermostat related improvements

[lorenc88]

I know that this component is not meant to handle thermostats but it works with them perfectly fine and in some cases it is far better than the original one. I would like to propose some tweaks that may make it even better.

1. Add property that will allow to change the step (for example halves of the value).
2. Add the ability to change the solid background color in relation to the value.
3. Add the ability to define the gradient. Could be based on CSS gradients.

Thanks for your awesome work!

[ndriu]

I also want to use it as thermostat and the step functionality is exactly what I need.

[GHeiner]

same for me.

[xeroxmsj]

Decimals would indeed be a nice upgrade!

[ricardoboss]

The first feature request is a duplicate of #79. Please go there and like it