Implemented spectrum for picking colors for the color picker pre-value e...

Utilises Spectrum colour picker library for the Prevalue editor of the Color Picker PropertyEditor.  A few things to note:
1. This may be a breaking change; as the selected colors include the hash (#) in the hex colors, and it's possible for the user to specify the colors in different formats at this time (including hsv() etc).
2. I've implemented an bg-color directive alternative to hex-bg-color as hex-bg-color was too restrictive and I didn't want to overly change the functionality without changing the name.  I also fixed a few typos in hex-bg-color and expanded it's validation check to allow for the hash in the color name.
3. Currently the view 'prevalueeditors/multicolorpicker.html' includes inline style on the pre element for better rendering, and I'd like to move these styles into a css file, but currently don't know where to put them.
4. Next steps may be to use Spectrum to pick the color from a drop down instead of clicking on a tile. Separate pull request for that one once I get it done :)