Add tooltips for new UI features

[kdahlquist]

As noted in #264, we need to add tooltips for some of the other new UI features, including normalization factor, viewport size, restrict graph to viewport/allow bounding box to expand features.

This isn't a super high priority right now, but I didn't want to forget about it.

[kdahlquist]

@mihirsamdarshi, this seems like something you could work on between now and the end of the semester.

[kdahlquist]

Elevating this issue for either @luluriffic or @igreen1--this would improve usability for GRNsight. We may need to discuss what the tooltips need to say at a meeting.

[dondi]

Possible candidate for a follow-up to a future bigger UI overhaul because newer frameworks make tooltip addition very easy to do.