use node type information to detect changes on protected properties

[dbu]

for example the nt:frozenNode has all properties protected in its node type. to have it work properly, we would just have to implement the node generically enforcing its constraints.

[dbu]

@danrot this is the thing we talked about yesterday. my idea would be that we add a method to item canEdit that is called whenever an operation is attempted that would edit the node and checks if this is a frozen node or a version, or if its a versionable node if it is checkedin.

but lets first get the versioning itself running.

[danrot]

Yeah, there might be some work left ;-)