Add tooltip on hover over hospital rating bars

[coxjonc]

Currently, a tooltip appears only when a user hovers over the filled-in section of one of the bars, not when they hover over the unfilled section. This creates a usability problem when only a small portion of the bar is filled in. The tooltip should appear when the mouse hovers on any part of the bar, filled or unfilled.

I'll try and submit a PR tomorrow when I get off work :)

[coxjonc]

Hey so I'd need access to your AWS config details to do the build and I guess it might be a little early to send those to me ;). Don't want to send a PR unless I can do a build and verify it works, but the issue should be easy to fix by making a small edit to this line in the chart_view.js script and changing rangeBars to bars, so that the tooltip is added on hover over the entire bar, not just the filled portion.