Initial version of a prev/next button for the web viewer
Moving nextPrevImage() to fix merge conflict
Ignore keystrokes on other inputs, sliders etc
Next and Prev ignore hidden thumbnails
Rename buttons to '< Prev' etc & semicolons
Disable Prev / Next if not available
Handle Prev / Next for search results and history page
Move Prev/Next buttons down below ROI count
Merge remote-tracking branch 'origin/develop' into prevNextWebViewer

Conflicts:
	components/tools/OmeroWeb/omeroweb/webgateway/templates/webgateway/viewport/omero_image.html
Merge pull request #2946 from will-moore/prevNextWebViewer

Prev next web viewer