show bottom bar on dashboard when there are no pipelines

[jamieklassen]

What challenge are you facing?

As a user when there are no pipelines, the bottom bar doesn't appear when I move the mouse or touch the keyboard. This means that I don't get to know what version of concourse I'm running! This would be handy information to have.

What would make this better?

Show the bottom bar when the user moves the mouse or touches the keyboard, but show a "reduced" one with just the version, justified to the right:

Are you interested in implementing this yourself?

👍 incremental value towards #2881

[jamieklassen]

@Lindsayauchin I left the CLI download icons on the bottom bar for consistency. If you decide it's too confusing to have the same actions in two places on the same page, we'll make another story to remove them from the bottom bar 😄