Adding component specs for Button, Checkbox, Icon, Link, Menu and Slider (#2134)

* Adding component specs for Checkbox, Icon, Link and Slider.

* Addressing feedback in review, fixing some errors in stardust props list, list of prop differences

* Another type, add todo on indeterminate state icon

* More fixes from spec review feedback: remove vertical

* Button: Adding Button spec.

* Adding Button spec.

* Adding Menu spec.

* Adding table to document & track conversion process

* Adding defaultChecked back in

* 1st spec done. :D

* Updating some other native props

Author: khmakoto