New design is bound to BrowserRootCategories collection

New design is bound to BrowserRootCategories collection. There are some bugs but we have something to show. Works correctly for Geometry category. Possible too long names of some functions. For example: `Geometry.Cuboid`.

@Benglin, please review.
It'd be nice to have more descriptive summary for all the new codes. For example, ```Group property``` does not tell a better story than ```public string Group```. It will be nice to explain what is this property meant for, and then what are some examples we can expect to see.