Imagej omero

Fix problems noticed while working on the integration of ImageJ2 plugins with @crueden
To test the PR, you first need to install imageJ server side
https://github.com/imagej/imagej-omero

Plugins currently only work on one image at a time, grey-scale (see https://github.com/imagej/imagej-omero issues for limitation)

To test the PR:
 * Test 1:
   * Select an image e.g. a png image
   * Go to the scripts menu, select imagej-omero menu. Go to process>Find Edges
   * The image ID should be populated
   * Run the script. An orphaned image will be created
 * Test 2:
   * Select a grey scale image
   * Select the process>Math>Substract
   * Make sure you can see the Value field (RDouble was not supported)