Nav Bar UI Revamp

Worked on making Nav bar look similar to wireframe here: https://wiki.openmrs.org/display/projects/ID+Dashboard+Wireframes#IDDashboardWireframes-Dashboard-Home/ExplorePage
Slightly changed design to make it more elegant.
I think this class actually need to be `btn-group btn-group-lg`. Right now, the btn-group styles aren't getting applied and the buttons look like they're having some weird border-radius problems :)