Restyled topbar to resemble UX guidelines

Also moved topbar styling into separate component
Adjusted context selection to match other dropdowns, merged it with topbar styles file

Partially-Implements: blueprint css-breakdown
Partially-Implements: blueprint navigation-styling
Change-Id: If30b85f5415a3e8d0416fdafeb233b722feb014f
Fix Horizon crash when parsing volume list

If using Nova or Cinder CLI to create a new volume
(without name) that can be used to boot a new VM,
then Horizon will be crashed when the volume list
is retrieved by clicking the tab "Volumes" on
Horizon dashboard.

Change-Id: I9850dca2f6f5ab8eebab035f9e7cf19d7262f7d2
Closes-Bug: #1389108
Merge "Restyled topbar to resemble UX guidelines"
Merge "Fix Horizon crash when parsing volume list"