The tag tree in screem version <= 1.1 isn't very well designed.
Currently it writes its data off using the normal Gnome configuration file
format.  This isn't a very good format for storing tree information.

As such I have decided that the tag tree will be stored using xml.  This will
make it very simple to construct the tree as the xml parser can build it,
then its just a simple matter of making a GtkCTreeNode for each node in the
xml tree.

This will also allow a child depth of more than 1.
The widget used will be changed from a GtkTree widget to a GtkCTree widget
as well.  this will also allow for nodes to have an icon to go with them.

As part of this the plan is as follows:

the tag tree will consist of:

+ HTML
| |
| + HTML 3.0
| | |
| | + tag group name
| | | |
| | | tag in that group
| | | |
| | | tag in that group
| | + next group name
| |   |
| |   tag in that group
| |
| + HTML 3.2
| |
| + HTML 4.0
|
+ User custom node
|
+ User custom node

Screem will be distributed with the HTML node and its children as standard.
The user can add any other nodes they want, such as javascript, php etc.
