Use 'renditionVisible' attribute of 'pictureConversion' XML contribution to hide picture views in UIs

XML contribution pictureConversion has an optional boolean attribute renditionVisible, it should be used in our UIs to show/hide picture views.

Visible picture views are returned by RenditionService#getAvailableRenditions, this list of visible picture views are also returned by content enricher renditions. This makes it quiet simple to hide picture views that are configured to be not visible.

Here is a sample Studio XML extension to make picture view FullHD invisible:

<require>org.nuxeo.ecm.platform.picture.ImagingComponent.default.config</require>
  <extension target="org.nuxeo.ecm.platform.picture.ImagingComponent" point="pictureConversions">

    <pictureConversion id="FullHD" renditionVisible="false" />

  </extension>

This should make the picture view invisible in our UIs.