Rationalize component and form APIs

[bradgessler]

Opening this issue to encapsulate various proposals that would be a breaking change and released in 0.6.x.

Related to issues and PRs:

• Rails Component interface kwargs uniformity #54
• Support overriding Superform::Rails::Form namespace #52
• Use kwargs for Rails::Components::BaseComponent #55
• Allow Rails::Form root namespace to be given a custom key #53

The one "rule" I'd write for "HTML-facing" code, like Form and Component classes, are that **kwargs keyword arguments are HTML elements. Non-html elements should be passed in via *args positional arguments or setters.

That means the PR at #55 would be merged and released in a 0.6.x breaking release.

The other proposal, #53, goes against this consistency since Form is an HTML-facing Phlex component; thus adding keyword arguments to the initializer would be inconsistent. One option is a positional argument, but my preference for this would be for developers to use a setter or subclass.

Details for each implementation will be in the respective PRs or issues. Respond to this issue for overall API consistency and change concerns.