Add loading state view to Route Summary view

[indraneel]

When selecting a Route to view its summary in the RouteSidebar component, the loading state view is pretty ugly.

Problems:

• if there was no previous route summary shown, the loading state view changes width when the data is finally loaded
• if there was a previous route summary shown, the component displays that view before loading the new data

Acceptance:

• show a loading state for all the UI items: total stops and each of the horizontal bar charts
• for the horizontal bar charts, hide numbers instead of showing NaN
• eliminate the width-changing jank when data state goes from loading to loaded

Optional:

• add animated/visually informative progress indicators