Clear model changes only as a result of load()

Also, clear changing the Titles on XhtmlModel items since their title
is never saved
Add serialize methods to models
Silently error when Model saving does not work
Workspace nodes show the path instead of "Untitled"
insertAfter now correctly uses the parent list of acceptable mediatypes
Merge branch 'dnd-drop-after' into github-refactor
Added a ToC pointer node that points to the module

so reordering leaf nodes works too
Merge branch 'github-refactor' of https://github.com/Connexions/atc into github-refactor
Merge branch 'github-refactor' of https://github.com/Connexions/atc into github-refactor