Exposure time

Fix issue reported by Damir see https://www.openmicroscopy.org/community/viewtopic.php?f=4&t=7555

To test:
 * Browse a plate. e.g. log in as user-4 plate ```INMAC384-DAPI-CM-eGFP_59223_1```
 * Select a well sample.
 * Go to the acquisition tab
 * Select a channel.
 * The exposure should be displayed and expanded by default.