Fix help tag which references OS X 10.6.
Work around more Yosemite control layout/metrics changes.

Make “Message:” and “Edit” wider (the latter was only cut off on Retina displays).

Move the calendar button over as it was rather non-WYSIWYG in IB.

The checkbox baseline of “Repeat” button is still off by one pixel, but not worth it.
Use non-bold font with no shadow in dock icon to better match Yosemite appearance.