Add test images for dayplots.
Fix crash when plotting events on dayplots.

event.picks only exists if event is downloaded from neries. If event is
just a dictionary of time/text, then it shouldn't be accessed.
Add more events to day plot test.

These don't currently work. The events are placed on the wrong line.
Add dayplot test with a catalog.

Also broken for same reasons as previous commit.
Updated reference images for dayplot tests.
Modify dayplot test to trigger other bug I found.
Fix rounding bug breaking previously added test.
Fix some typos in docs and comments.
Merge branch 'master' into dayplot-tests
Merge pull request #767 from QuLogic/dayplot-tests

Dayplot error when giving the events argument