Get rid of long module paths, make the hierarchy more flat

[wokalski]

This is not visible when you build the library but extremely annoying when you build an app with Brisk. Currently there are many constants hidden away from the user, like Cocoa.BriskButton.BezelStyle.TexturedRounded while Button.Style.TexturedRounded would be much more optimal. Or maybe even something shorter.

It's also hard to discover. We have many constants like that for Image, Button, Text which need to be organised better. This issue is for finding a systematic way to organise them and implementing this organization.

One interesting technique might be:

type t = Brisk.LongModulePath.ItShouldBeThere.t = 
  | ReexportedValues;