Help link (rebased onto develop)



This is the same as gh-1618 but rebased onto develop.

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Point help to help.openmicroscopy.org instead of the feature list

Both web and insight have been updated.
see https://trac.openmicroscopy.org.uk/ome/ticket/11502

To test:
 * Open insight, go to the help menu. Click on the link this should bring you to http://help.openmicroscopy.org/
 * Repeat the same for web.