Add a skeleton for Palm4MSAFFT with the two methods to override from parent...

Add a skeleton for Palm4MSAFFT with the two methods to override from parent class Palm4MSA: compute_grad_over_c() and compute_lambda().

- Also completing the baseline test (test_palm4MSAFFT.cpp.in), and
- ParamsPalmFFT parameters for initialization of default init_D (eye() matrix).