Adding function to plot majoron spectrum

Function added to plots.py to format and produce spectral plot for Majorons.
Also includes an additional function in error_utils to check if two values are
equal to a given precision. This is employed in isotope.py to ensure the sum of
the masses of each scintillator component equals the mass of scintillator.
Modifies KLZComp.py

Adds error checking to check that the combined KLZ background has same bin
width as two_nu, so they can be added. Also uses more events "100k" and adds
minor changes to help text.
Merge branch 'KLZComp'
Modifies .gitignore to not track src/generate/from_paper
Submodule utils_cm

Moves utils modules shared with another repo ashleyrback/DQ to a new repo
utils_cm. Adds utils_cm as a submodule of MajoRat.

Files affected are:
 * src/util/error_utils.py
 * src/util/file_manips.py
 * src/util/list_manips.py
 * src/util/string_manips.py
all of which are now in src/utils_cm/
Adds minor modifications to gitignore