Fix 2px date clipping and make date/time headers a little more readible

I fixed the 2px date clipping by setting the width constraint to the current width in the canvas (but there may be more clipping in the future if the width isn't wide enough to accommodate all the different dates).

The current font size for the daily time total is kind of small and hard to read (as mentioned in toggl/toggldesktop#169), so I bumped it up to 11 (from 9) and set the date size to 14 to try to maintain the visual relationship between the date and time.

I might try to find a solution that splits up the days a little better visually (this might be related to toggl/toggldesktop#170?) because it's a little more difficult than it should be to quickly parse it at a glance.