modal day fixes for release

A few fixes requested by @brandonarbiter for first release of modal day. @ianjorgensen it'd be fantastic if you could take a look today so that I can build my tomorrow morning.

Fixes include:
- I'd removed tooltips on hover on an smbg value when data was grouped, but it was actually easy to add them back on BA's request; the task of adding back the hovers on a line (so you get the entire day's readings in tooltips) is a bit harder when data is grouped, so I'll save that for later
- when there is less than 90 days smbg data for modal day view, the ticks generated for the mini scroll bar will generate centered dates (at 1-week or 2-week intervals depending on how much data there is) instead of right-anchored month names
- removed log scale for BG data in one-day view
Added variables.