Add a function to show segmented particle images/masks as montage

[YichiWang]

Plus some .pyc cache files and parameter.h5 file were manually chosen to be ignored because they cannot be ignored automatically on my PC.

[codecov[bot]]

Codecov Report

Merging #51 into master will decrease coverage by 2.66%. The diff coverage is 12.90%.

@@            Coverage Diff             @@
##           master      #51      +/-   ##
==========================================
- Coverage   80.99%   78.32%   -2.67%     
==========================================
  Files          13       13              
  Lines         784      812      +28     
==========================================
+ Hits          635      636       +1     
- Misses        149      176      +27     

Impacted Files	Coverage Δ
ParticleSpy/ptcl_class.py	65.51% <6.89%> (-11.73%)	:arrow_down:
ParticleSpy/ParticleAnalysis.py	93.92% <100.00%> (-0.03%)	:arrow_down:

[TomSlater]

This has broken things for me. The first particle has an image stored correctly but all others just have zeros.

I'm not sure I follow all of your changes in terms of the background subtraction and the boxing/padding. Are you sure this is all correct?