Document new OpenAstexViewer configuration options

[cxallan]

In #6919 new configuration options were added for the OpenAstexViewer?. These should be documented on:

http://www.openmicroscopy.org/site/support/omero4/server/install_web

as in the "Controlling displayed scripts" section denoting the version number (4.3.3) since the options have been available.

[wmoore]

Added this to page above:

Since OMERO 4.3.2 OMERO web has included the Open Astex Viewer, which is a Java Applet for viewing volume surfaces. See the [Open Astex Viewer](http://www.openmicroscopy.org/site/products/omero/products/omero/volume-viewer-in-omero.web) introduction. Scipy is used on the web server to down-sample large images for viewing in the web. Since OMERO 4.3.3 it has been possible to limit the size of Images that display the 'Open Astex Viewer' icon, so as to prevent users attempting to open large images (poor scaling performance). The size restrictions are based on maximum number of voxels and maximum & minimum length of X, Y or Z sides. The default values are a balence between functionality and performance, but you may wish to increase the threshold a little to view particular images. NB: These values only affect the size of images that will be scaled by scipy. If scipy is not available on the server, no images above 160 x 160 x 160 will be viewable in the Open Astex Viewer.

                $ bin/omero config set omero.web.open_astex_max_side 500             # default is 400
                $ bin/omero config set omero.web.open_astex_min_side 50              # default is 20
                $ bin/omero config set omero.web.open_astex_max_voxels 15625000      # default is 27000000 (300 * 300 * 300)