Make Input component more useful (respects error prop declaratively)

[romeovs]

I've changed the way the and Input component decides whether there is an error or not.

Input doesn't have any state related to errors any more. Instead the error is hold completely inside props.

Some examples:

// this will show an error
<Input name="input" error="this is an error" />
// these will not show an error
<Input name="input" />
<Input name="input" error={undefined} />
<Input name="input" error={null} />

This is more declarative than having to call setError and removeError and allows components to
use the Input more concisely.

Additionally I also made type="text" default for the Input (although this is something debatable).

[hai-cea]

Thanks @romeovs ! Fixes #95

[mikepb]

error != null matches both undefined and null

[mikepb]

Better to use:

  componentWillReceiveProps: function (nextProps) {
    if (nextProps.error) {
      this.setState({
        error: nextProps.error
      });
    }
  },

[romeovs]

I'm not a frequent React user so I might be confused here, but I recall reading that using prop values for the state of the component is bad because it duplicates the "source of truth" (eg. all info is there in the props, so why pull it into the state?).

[mikepb]

Yes, removing the set/removeError methods would most idiomatic.