Improve Save Animation Settings Dialog

This removes the spin box from the start and end frame settings
and replaces it with a line edit. Also sets the default frame
rate for animations to 15 fps.

Change-Id: I907b303569aec97d1dc8c53c0655b77bb7d7f937
Merge topic 'save-animation-dialog' into next

e8ce209 Improve Save Animation Settings Dialog