Channel edit

Implement channel edit.
See https://trac.openmicroscopy.org.uk/ome/ticket/10022

To test: 
* Edit channel of one image. Click Save
* Browse a dataset and edit channels of an image and click "Apply to All"
* Browse a plate and edit channels of an image and click "Apply to All"
* In both case a warning message should be displayed.
   * Click Save.
* Click Cancel to abort the edit, make sure the original display is reset.
* Select an image, open the viewer. Edit the channel. Click Save. Check that the channel values have been updated in right-hand panel and in the viewer.

This PR also fixes https://trac.openmicroscopy.org.uk/ome/ticket/10096 and https://trac.openmicroscopy.org.uk/ome/ticket/10041 (similar problem)