customizing 'Orphaned images' container

This PR allows to customize name and description of 'Orphaned images' container. This is particularly useful if DropBox is set and 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)