Adding more non-linear timing and red noise PL plotting utility

[ark0015]

This request adds the ability to plot a broken powerlaw with two breaks (extra broken powerlaw) in addition to several additions to help support the TimingCore:

• Simplified convergence checks
• Summary comparisons of timing parameter posteriors to original timing model parameters
• Simplified corner plotting
• Residual comparisons between sampled timing model and original timing model
• Ability to compare the overlap of multiple chains from runs with different parameters
• Mass parameter plotting for binary pulsars
• Misc. utility functions (selection of subgroups of parameters to plot, creating a .dmx file from a parfile, etc.)