Removed invocation of BRJS.setFileModificationService() from directly
within a test and used TestModelAccessor to do this instead.
Deleted the FileModificationServiceNodeReadyObserver as it was slowing
down the `build-app` command, yet removing doesn't seem to have led to
any bugs.
Stopped invoking resetLastModified() in the constructor as this now
causes the timestamp of all ancestor objects to be reset too.