TA-1545: Further branding updates

[klaudija-lawrence]

https://techfromsage.atlassian.net/browse/TA-1545

Further changes are required to our branding styles. The following changes have been made here:

• Using turquoise tint for the navbar with a blue bottom border
• Using inquisitive blue for hover states in the nav bar
• Updated dropdown hover states
• Updated link color and text-decoration to be in line with new designs
• Removed some unnecessary comments

The changes can be seen in the kitchen sink when running npm start and also in the DC app by updating bower.json to have "bootstrap-sass": "talis/bootstrap-sass#TA-1545_update_branding" and rebuilding the app.

[pogotc]

LGTM