Improve component prop documentation

[JakeSidSmith]

Makes it obvious that passing a function to the component prop does not treat it like a render prop, and it is in fact a component.

Previously not explicitly referring to this as a component and using camel case naming implied that this prop was treated as a render prop, and not rendered with React.createElement as stated just above.

I have used the same naming as the class component example, and appended "component" to references of "stateless function".

This has the added benefit that, when necessary, these components can be used without redux-form due to the capitalized first character e.g.

<MyField />

I've also changed "normal component" back to "class component" as both styles are equally "normal".

[codecov-io]

Codecov Report

Merging #4699 (c8e44f0) into master (f8b721b) will not change coverage.
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