style(dates): make date markers pretty

[johngruen]

This should get merged after #340

[pdehaan]

Figure 1: The bottom of the date marker is a bit touchy on the first history item.

[johngruen]

@pdehaan gap issue fixed!

[pdehaan]

Much nicer! I'll need to tweak my local data some more since it seems to enter all the visits for the same day, but I did notice a super edge case where you spend 4 minutes deleting all your visits, the date header still remains. But we can file that as a separate issue and handle it later.

Figure 2: Date header remains after you delete all your visits.

[pdehaan]

Possibly less edge case? I hacked my ./bin/create_test_data.js to create data for random days and then I deleted items and it looks roughly like this. Actually, probably the same issue as my previous comment, just funnier results with multiple stacked day labels:

Figure 3: January 4th January 3rd January 2nd

[nchapman]

Hooray! :+1:

[nchapman]

Date header remains after you delete all your visits.

@pdehaan will you create a new issue for this?

[pdehaan]

@nchapman Filed as #350