Flexible modes and much more

[KSkwarczynski]

List of features

• Add flexible modes, MaCh3 code relies on modes (CCQE, RES) etc. however each experiment has different need addionaly due to use of diffent gernetaros mode are different hence new class MaCh3_Modes was added
• Update MCMC processor which can genreically plot psoteriors
• Significantly speed up spline monolith
• Tidy CMAKE build
• add Akima splines etc.
• Fix memory leaks in covariance classes
• Minor improcments to FD Base class