Refactor asInput

[thallada]

Over time, asInput has grown a lot to support many features. It could be split up more to compose itself out of smaller sub-components. Part of this work was done by extracting the validation message out into a ValidationMessage component. We could also make Label and InputDescription components, for example. Exporting these components to Paragon users would also allow them to compose their own custom input components if asInput does give them the flexibility that they need.

See reactstrap for examples of how granular the sub-components could get (basically one component per HTML div). Internally, Paragon could build asInput out of these more granular components so that users of Paragon could use asInput to create basic inputs quickly, but also use the granular sub-components if they need more customization than asInput provides.

There are some special-cases for checkboxes, but not for radio buttons. That part could be a bit more abstracted.

[abutterworth]

asInput has been replaced by React Bootstrap Form components #550