Added the ability for keys to copy themselves during pipeline passes.
This allows arbitrary meta-data to flow back and forth in the pipeline
with changing the executives. Although this is similar to KEYS_TO_COPY,
it works significantly better. KEYS_TO_COPY has one major flow: it
does not work if the algorithm that is supposed to add the key to
KEYS_TO_COPY already executed and a filter downstream is causing re-
execution.

Also added the ability for keys to store meta-data in a data object's
information. Allowing them to check it later in NeedToExecuteData.
This allows filters to send a request upstream to potentially cause
a new execution of the pipeline with changing the executives. This was
not possible before.

This was done by adding 3 new virtual methods to vtkInformationKey:
NeedToExecute(), StoreMetaData() and CopyDefaultInformation(). Normally
these do nothing. Subclasses can overwrite them to implement new
behavior. These methods are called by the pipeline at certain times.
CopyDefaultInformation() is called during CopyDefaultInformation(),
StoreMetaData() after execution (REQUEST_DATA), NeedToExecute during
NeedToExecuteData.

Change-Id: Ice192eb0be9f0a47b512c1b0fa3cfbede74d81e1