[QUERY] APPLY functions to node, e.g. for adding/removing node types

[dantleech]

Maybe we could do this by using the function mapping discussed in #90

UPDATE [nt:foo] APPLY nodetype_add('nt:barbar')
UPDATE [nt:foo] APPLY nodetype_remove('nt:barbar') WHERE x
UPDATE [nt:foo] APPLY do_something_copmpletely_different() WHERE y
UPDATE [nt:foo] APPLY nodetype_add('foo:bar'), property_set('foo', 'bar'), nodetype_remove('bar')

[dantleech]

One really interesting application of this would be for migratin node types.

This would normally be done with setPrimaryType but this is not implemented in Jackalope yet, and more seriously not supported by Jackrabbit.

Such a function would mv the target node to a tempoary location create a node with the new type and then attempt to add the children of the old node to that node before deleting the original node.

UPDATE [nt:foo] AS a APPLY TO a migrate_primary_type('nt:newtype');

[dantleech]

Addressed with #125