Sort out the refactoring framework

The refactor actions (rename/move/rename-namespace/delete) have been organically developed and patched over the course of several years and as such lack a consistent approach in their operations.

Re-implement the logic of each action using Eclipse's refactoring framework. This will include the following features as a standard part of the implementation:

• Ties into Eclipse's history framework so resources can be restored to a previous state
• Provides a UI so that the user can preview and accept the changes prior to them being performed
• Sensible separation of condition-checking and actual operation
• Functions in the same manner as existing Eclipse refactoring functionality