Add counts / weighted counts per particle type

[maxnoe]

adds n_{electron/proton}{,_weighted} in the sensitivity table (Results look ok)

[codecov]

Codecov Report

Merging #108 into master will increase coverage by 0.18%.
The diff coverage is 95.34%.

@@            Coverage Diff             @@
##           master     #108      +/-   ##
==========================================
+ Coverage   89.25%   89.44%   +0.18%     
==========================================
  Files          36       36              
  Lines        1201     1241      +40     
==========================================
+ Hits         1072     1110      +38     
- Misses        129      131       +2     

Impacted Files	Coverage Δ
pyirf/sensitivity.py	90.76% <75.00%> (-1.30%)	⬇️
pyirf/binning.py	97.10% <90.00%> (-1.21%)	⬇️
pyirf/tests/test_binning.py	100.00% <100.00%> (ø)
pyirf/version.py	100.00% <100.00%> (ø)

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