[OnDemand] Update rteolayer to use lxml

A good few changes to rteplayer.py
- Mainly use lxml to retrieve the feeds
- Update to categories to also show a thumbnail
- Change location for default icon if show images is false

A small change to threeplayer.py
- Change location of the default icon if show images is false

A general tidyup on tabs in rteplayer.py and default.py also