`changed` state for input fields

[mbohal]

Presently input fields support optional prop validationState that takes values valid, invalid, warning that correspond to colors green, red and yellow respectively.

Now we nee a new state changed that will be indicated by yet another color.

[mbohal]

I think there are several approaches how to handle this.

1. Adding a new validationState value
2. Reusing the valid state to indicate changed.
3. Adding a new prop changed
4. Renaming validationState to something more generic (e.g. state) and adding the new option changed
5. Just use color prop with the palette that is used everywhere

My take on these:

1. Is strange as changed has nothing to do with validation.
2. is wrong as being changed has nothing to do with being valid. Also the valid state could be useful although we do not use it presently.
3. would require us to handle situation where both changed and invalid / warning / valid are used. I think we could assume that validationState beats changed in priority. However adding another prop makes the API more complex especially with the "hidden" rule of validationState taking priority over changed.
4. Is a breaking change and is less flexible then 3).
5. It allows using needlessly rich color palette that could lead to confusion if not handled properly.

I think we should decide between 3) and 4) and 5). I do not have strong feelings for either one of these approaches.