Allow setting initial day of week text length

[bruceharrison1984]

Is your feature request related to a problem? Please describe.
The default internal size of the calendar is currently large. This means if you load the calendar into a small container, the initial render will display the long names of days instead of the short names. This looks bad, and there should be a way to specify the starting size of the calendar.

Describe the solution you'd like
An additional initialDayOfWeekLength prop should be added that allows users to set the default size of the component to minimize this UI bug. I don't think it can be completely fixed, but this should make it easy to sidestep and avoid ugly UI flashing.