Use less hard-coded colors in favor of theme colors.
- We were using some off-brand colors like "green" instead of UbuntuColors.green. Which are now fixed to the theme 'positive' color in this branch anyway. - We were using a lot of orange in places we shouldn't (mostly for recommended buttons, some selected states, and in one place for a progress indicator). - We were frequently specifying the color of a neutral button, but never the same way twice (coolGrey, warmGrey, lightGrey). No need, the default button color should be fine. - And I fixed a few of the instances of UbuntuColors.darkGrey for text to appropriate theme colors. (LP: #1581047)