Change peak properties to be based on molecule names

[MKoesters]

this allows to write two different (or same) molecules with the same chemical formula

• key in peak properties is now molecule name
• add new key chemical_formula in peak_properties dict
• adapt all tests and example scripts to new data structure
• execute all example scripts in tox
• add min intensity in mzmml_params to remove extreme small intensities generated

[codecov]

Codecov Report

Merging #32 into dev will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##              dev      #32      +/-   ##
==========================================
+ Coverage   99.61%   99.62%   +0.01%     
==========================================
  Files          16       16              
  Lines         770      805      +35     
==========================================
+ Hits          767      802      +35     
  Misses          3        3              

Impacted Files	Coverage Δ
tests/test_lib.py	100.00% <ø> (ø)
smiter/lib.py	100.00% <100.00%> (ø)
smiter/params/default_params.py	100.00% <100.00%> (ø)
smiter/synthetic_mzml.py	98.60% <100.00%> (+0.14%)	⬆️
tests/test_synthetic_mzml.py	100.00% <100.00%> (ø)
smiter/fragmentation_functions.py	100.00% <0.00%> (ø)

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