Default Function values

This ticket implements default function values.  You may now set a default function in both the object or through the InputFile.  

Case 1: A string is set in the addParam function or read from the input file:
A FunctionParser object is created to see if that string can be parsed into a function, if it can, a new MooseParsedFunction is constructed through the Factory and set in FEProblem like any other function.  

Case 2: An int or Real is used in addParam or read from the input file:
That value is converted to an string and goes through the same logic as above.  A constant function will always be generated in this case.