Preview panel like insight

This adds rendering settings to the web client Preview panel (like Insight).

 - Web preview panel has same (or very similar) rendering controls as Insight
 - All changes are 'applied' immediately (no "apply" button).
 - Reset, min/max and full range settings are not saved and can be reverted by undo/redo.
 - Settings can be copied and pasted between Image viewer, Preview panel and P/D/I tree (right click menu).
 - Other users' settings can be applied without saving.
 - Only on 'Save' or 'Save to All' are the changes saved and thumbnail updated.
 - The main image viewer rendering panel is also more compact (looks neater and allows more code reuse with Preview panel).

To test:
 - Open Preview panel and change rendering settings via:
   - Channel toggle buttons
   - Sliders
   - Start/end inputs (either end of sliders)
   - Color picker
   - Copy/paste
   - Min/max button or full-range button
   - reset button
 - Check that Changes are applied automatically and not saved
 - Undo and Redo changes and check all changes can be undone.
 - Save and check that thumbnails are updated in centre panel and for 'your' rdef button.
 - Save All and check thumbnails.
 - Check that right-click menu works for:
   - Reset rdefs for Datasets / Images.
 - "Launch full viewer" button should use current settings
 
 - Also need to test Full viewer, checking that all settings changes are shown immediately (no "Apply") and that Undo, Redo and Save work as expected.

TODO - "Save All" not working for Plates (same for renaming Channels).


To discuss:
 For all right-click menu "Apply and Save" options, should we have a confirm dialog?
 Insight to add Copy / Paste buttons to Preview panel.
 Insight to add ROI count to Preview panel?
These docstrings need to be converted to Sphinx markup - see http://ci.openmicroscopy.org/job/OMERO-5.1-merge-build/ICE=3.5,label=ome-c6100-3/javadoc/python/omero/omero.gateway.html#omero.gateway._ImageWrapper.getAllRenderingDefs