Change component parameter declaration programming model

[danroth27]

@rynowak here filling in the details

In 0.3 we are changing how component parameters are defined to require the use of [Parameter] (ParameterAttribute). While we're introducing ref for capturing component references in this release, it makes sense to change the design of component parameters in a way that encourages encapsulation. We want to strongly encourage everyone to use markup to set the properties of components, rather than setting properties directly. This is more efficient, and will make sure that the correct rendering sequence takes place.

To that end, we've added an analyzer in 0.3 that will recommend that you make component properties private.

The requirement to add [Parameter] will also apply to things set by the framework such as ChildContent or Body (layouts) and parameters set by routing.

[rynowak]

Self assigning this as I'm getting started on part of it.