UP-4337: Complete the Dynamic Respondr Skin portlet

https://issues.jasig.org/browse/UP-4337

Kept the primary and secondary color choices, but removed the third color from the picker.

Added color selection to:
- Link text
- Footer text color
- Footer background
- Portlet border color (header and body)

Modified the appropriate *.LESS files for color updates.

Added these color preferences to portlet.xml, along with adding the appropriate labels in Messages.properties (English).

Rearranged the Dynamic Respondr Skin portlet into two columns, three colors each side (more room for labels)

Please keep reminding us @apetro :smile: .  The broader solution may be better to wait until we get more options to make it more worthwhile, plus an opportunity to fund the development.  For the short to mid term though I think portlet preferences is a low cost reasonable solution.  

As a side but possibly related note, I created an issue https://issues.jasig.org/browse/UP-4355 about providing a user profile editing page that portlets can participate in so uPortal can provide a more typical web site experience where a user can configure their site preferences.  I wanted to get some exposure to that idea for hopeful synergy in collaborative brain storming, and to tie it into this because I can see certain skin preferences (integrating background changer into a skin preference as one, choosing rounded vs. non-rounded corners, etc) as possibly user preferences that any user can change.