The block parameter should always be valid

[aeslaughter]

Block restricted objects rely on the "blocks" parameter, which should be populated if not defined. Derek proposes adding a BlockRestrictedInterface to enable this behavior for all objects that should be restricted.

[aeslaughter]

I attached a patch that implements and tests a BlockRestrictable class that is inherited by any object that you would like to user the 'block' input parameter. Someone should take a look at it and see if this will work.

Two things that I believe still need to be addressed are:

• The SubdomainIDs are passed using std::set and std::vector in MOOSE and libMesh, it seems like we should pick one and be consistent (if possible). Currently the BlockRestrictable class in this patch attempts allows you to use either.
• Some objects, Postprocessors, default to ANY_BLOCK_ID. This seems like it should be the default for all objects. It seems that currently in MOOSE and empty block is the same as ANY_BLOCK_ID, I think we should pick one and use this new class to control the behavior.

[aeslaughter]

In 40bcede:

Created BlockRestrictable class for restricting objects to block ids (closes-#2096)