Evaluate Tools folder structure.

[MrDinsdale]

Is your feature request related to a problem? Please describe. Structure is a little cluttered/inconsistent with some files for mixins and functions and some ui specific ones with a mix. For example the reverse() function only used by gradients is actually in functions.scss, the location of such tools shouldn't have any ambiguity.

Describe the solution you'd like A more consistent structure for our Tools so that it is immediately apparent where to find them.