* move last_group_node to DirectoryNode
* move add BaseNode:as and more doc
* revert parameter name changes
* revert parameter name changes
* add Class
* move group methods into DN
* tidy group methods
* tidy group methods
* tidy group methods
* tidy group methods
* parent is DirectoryNode
* tidy expand all
* BaseNode -> Node
* move watcher to DirectoryNode
* last_group_node is DirectoryNode only
* simplify create-file
* simplify parent
* simplify collapse-all
* simplify live-filter
* style