Majoron limits

[ashleyrback]

Supersedes #56

Changes include:

• Adds echidna.__echidna_base which points to base directory of echidna repo
• Adds to constants, including some SNO+ defaults
• Modifications to decay methods, mainly some re-naming and re-structuring. Also adds better handling of ROI efficiency.
• Adds physics tests in decay.main, which test compatibility against Andy's numbers (numbers from docDB)
• In Spectra class:
  • Adds shrink_to_roi which, given an axis, lower and upper limit for an ROI, calls the standard shrink method and also calculates the efficiency (roi_integral / full_integral) and stores the parameters in the dict Spectra._rois[axis].
  • Adds getter/setter methods to save plotting style information in Spectra._style
  • Adds cut method which is similar to shrink but updates Spectra._num_decays, meaning that the Spectra object represents a different number of decays after calling this method.
• In chi_squared:
  • Adds set_penalty_term method
  • Chi squared calculations now calculate chi squared per bin, accessed via get_chi_squared_per_bin
• Adds counts_down and corresponding get_last_bin_above methods, plus a few other helpful methods.
• Adds lots more useful content to SystAnalyser class
• In LimitSetting:
  • Adds debugging tool which produces a catalogue of spectral plots via matplotlib'spdfPages
  • Functionality to add a target spectrum (e.g. limit set by another experiment). This can be shown on (debugging) spectral plot(s) to compare limits.
• In plot module:
  • Adds spectral_plot method to produce spectral plot
  • Removes import of pylab in module
• Adds more useful plotting methods to plot_chi_squared, including "trun_on" plot and "push_pull" plot. These are all useful diagnostic tools that help visualise the data collected by the SystAnalyser class.
• Bug fix in store.load/dump_ndarray
• Adds (example) limit setting scripts for SNO+ Majoron modes and Majoron modes in Xe136
• Adds physics_tests module

[ashleyrback]

@jwaterfield docs should now be fine too. except for a couple of problems displaying maths in decay module. I can't quite figure out why as they were displaying fine before and haven't been changed.

[jwaterfield]

Ok. Happy and merging