Add render method to Component and auto implement Renderable

[jstarry]

Fixes: #339

[hgzimmerman]

As a thought, to make this a non-breaking change, you could define a FullComponent which is the superset of Component with the added render function and blanket implement impl <T> Component for T where T: FullComponent and impl <T> Renderable<T> for T where T: FullComponent.

I understand that you are opposed to aesthetic-only features, but something like this would allow avoidance of breaking everyone's code, and normalize the existence of something like PureComponent should you choose to include that.

The obvious downsides would be confusion related to differences between FullComponent and Component, and the fact that the dominant Component interface just gained four extra letters.

It might be possible to deprecate Component, then making it private to Yew (something tells me the typesystem may not be fond of this), forcing eventual migration over to FullComponent, Component could be renamed to something like ComponentInternalImpl, and FullComponent could be transitioned in the same way to become Component. So over the course of 5 or so releases you might be able to accomplish a gradual migration back to the normal, minimal trait name with deprecation warnings instead of a single breaking change.

Trait name migration plan:

1. Add FullComponent and deprecate Component.
2. Make Component private, forcing downstream crates to switch over to FullComponent.
3. Reintroduce Component which blanket implements FullComponent, rename old Component to ComponentInternalImpl.
4. Deprecate FullComponent.
5. Remove FullComponent, change blanket for Component to blanket impl ComponentInternalImpl.