Tempo2Pulsar is not units aware

[vhaasteren]

Tempo2Pulsar does not know what units the parameters and the designmatrix have. If one just marginalizes over timing model parmaters, that is not important. But if one is interested in the timing model parameters, the design matrix and the timing model parameter units need to match. Moreover, the units need to be known for comparison with PINT or other values in the literature.

Supporting this will require working together with libstempo to support it there as well.