Fix 24h display when showMeridian is false.

This pull request adds a simple padding method for use when showMeridian is false and elsewhere. I added one extra spec for testing. 24 hour times should now have double digits on display. This should fix #208.

I also noted that the pull request #203 did not actually set the display, only the underlying values. In my opinion, this pull request has a cleaner and easier to read solution.