Central dashboard should be left handed navigating bar

[jlewi]

We'd like the central dashboard to be a left handed navigation bar. On the right panel we'd like to eventually show different cards e.g. "quick launch a notebook."

Related issue: #2092 fix color scheme for central dashboard

We should come up with some form of mocks to look at it before making the changes.

[cwbeitel]

What if you made the pipelines UI the primary UI? You could embed the notebook spawner UI within a notebooks section without linking out to another page.