customizing 'Orphaned images' container

This PR allows to customize name and description of 'Orphaned images' container. This is particularly useful if with DropBox setup where newly imported images are coming in.

```
$OMERO_HOME/bin/omero config set omero.web.ui.tree.orphaned '{"NAME": "Trash", "DESCRIPTION": "This is trash."}'
```
![firefoxscreensnapz003](https://cloud.githubusercontent.com/assets/1065155/2577307/0a303d20-b97e-11e3-8636-28e517c41500.jpg)