Correction to BDM degree method

Correction to BDM degree method

* The documentation says this function should return one less than
    the highest polynomial degree. This is consistent with the
    notation used in the literature on BDM polynomials and is what I
    would expect the function to return.
* However, the function actually returns the degree of the highest
    polynomial degree because it calls PolynomialSpace.degree() (note:
    in this context, PolynomialSpace is the complete polynomial space
    of degree k, next then we add elements from k+1 to complete the
    BDM space) which specifically states it does not return the
    Maxmial degree of the polynomial, but the number of polynomials
    given to the constructor.
* If I understand correctly, since the number of polynomials given
    to the constructor includes constants, this returns degree+1.
* To correct this, one needs to be subtracted from the degree of the
    polynomial_space.
* A typo in the 3D bdm_grad functions has also been corrected
* Made a correction in the compute method to reflect the change in the
    degree method.
* Corrected out in the test polynomials_bdm_01.output file
* Edited some names in the test bdm_1.cc