Fix for ticket #717.

Fixes a bug introduced by the MMStudio/MainFrame split that caused the "sync
main frame and MDA exposure times" option to be one-way only.

git-svn-id: https://valelab.ucsf.edu/svn/micromanager2/trunk@14402 d0ab736e-dc22-4aeb-8dc9-08def0aa14fd