SystemEditor is a mechanism for atomically loading a set of changes to the system.
It's intended to be used by tools such as that move classes (or parts of classes) between
images, such as Monticello, Monticello2, change sets, fileIns etc.
It provides a familiar interface for making changes, but does not execute the changes
until it receives a #commit message. This makes it easier to update existing tools
to load their changes atomically.