Add Ideal Browser Support

[brennanmceachran]

Is this a latest version of modern browsers only thing? Or are we aiming to support ie8+?

[ldoubleuz]

This library is built on x-tags, so for now, we can use those as the ideal support. (However, the exception is anything with flexbox, like x-layout or x-togglegroup will require IE10).

I'm hesitant to claim stable support for them in light of some of these bug reports, but these are the ideal at least.

[umhan35]

I think we need to put this information somewhere explicitly.

[potch]

Testing grid support (coming in Brick 2) will answer these questions definitively.

[potch]

Tracking this in #222.