Let FEProblem return a vector of OutputName based on the output type passed in

[YaqiWang]

I think this request is reasonable. We can add something like

std::vector<OutputName> FEProblem::getOutputNames<Console>();
or
std::vector<OutputName> FEProblem::getOutputNames(MooseEnum output_type);

so in the actions, I can assign this names to the parameter outputs of a postprocessor.

[aeslaughter]

• I did implement the ability to return an object by name today:
  OutputBase * = _app.getOutputWarehouse().getOutputByName("my_postprocessor_outputter");
  You will then need to cast this to the correct type, put perhaps we should have a template method that performs the cast automatically.
• That being said, I think that @YaqiWang's idea is good. However, it would go inside of the OutputWarehouse, so you would call it by:
  _app.getOutputWarehouse().getOutputNames<Console>();
• I also vote for the first option, we don't want to maintain a list of output class names since the idea is that users can create there own.
• If users are going to start doing this type of thing, do we need yet another interface: `OutputInterface' that would provide this type of access?

Does anyone else have an opinion on any or all of this?