The colors defined in `colorutils.js` are specified in
fish format, and therefore RGB values lack the leading
`#` character and do not fully follow the html/css spec
(w3.org/TR/css-color-4/#typedef-hex-color).
Web config sends these values as-is to the browser,
without first converting to a browser-friendly format.
While this (somehow) works for the most part, a few
colors get lost along the way and do not display in
the customization selector nor in the preview when
selected. This behavior was seen in Firefox.
To fix this, let's prepend the missing '#' character
to all RGB colors defined in `colorutils.js`.
Since the url is inside a AngularJS markup {{url}}, it's better to use **ng-href**.
From [AngularJS Documentation](https://docs.angularjs.org/api/ng/directive/ngHref):
<br>
"Using AngularJS markup like {{hash}} in an href attribute will make the link go to the wrong URL if the user clicks it before AngularJS has a chance to replace the {{hash}} markup with its value. Until AngularJS replaces the markup the link will be broken and will most likely return a 404 error. The ngHref directive solves this problem."
This is meant to make it clear that fish cannot control the terminal
window background color. It also augments the set_color documentation to
describe how it decides which color the terminal can display.
Resolves#2421.
Resolves#2184.
* Show color scheme title in preview box
* Show information about setting terminal background color on Apply
button mouse hover
* Added text_color_for_color method in colors controller scope
