Changes to allow customized properties and impact item creation

[yalinli2]

The changes are minor, but since they are to the basic classes so I wanted to make sure I'm not messing things up. One is to add a dictionary in WasteStream (addtional_properties) so that users can throw in whatever properties they want, like turbidity, etc.

Another is to allow the creation of StreamImpactItem through the load_from_file function, this way you can put all CFs together in one spreadsheet.

All the tests are passing locally, but I realized metab doesn't have a test file, so just want to make sure the updates aren't breaking your stuff @joyxyz1994 , thanks!

[codecov[bot]]

Codecov Report

Merging #109 (dece5c5) into main (946bf48) will decrease coverage by 1.57%. The diff coverage is 21.73%.

@@            Coverage Diff             @@
##             main     #109      +/-   ##
==========================================
- Coverage   75.46%   73.90%   -1.57%     
==========================================
  Files          90       91       +1     
  Lines       15705    16003     +298     
  Branches     1675     1688      +13     
==========================================
- Hits        11852    11827      -25     
- Misses       3379     3704     +325     
+ Partials      474      472       -2     

Flag	Coverage Δ
unittests	73.90% <21.73%> (-1.57%)	:arrow_down:

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
qsdsan/processes/__init__.py	100.00% <100.00%> (ø)
tests/test_exposan.py	100.00% <ø> (ø)
qsdsan/_component.py	91.86% <90.90%> (-0.25%)	:arrow_down:
qsdsan/_waste_stream.py	86.44% <83.33%> (-0.05%)	:arrow_down:
qsdsan/_impact_item.py	70.80% <60.00%> (-0.27%)	:arrow_down:
qsdsan/utils/cod.py	70.34% <0.00%> (-0.21%)	:arrow_down:
qsdsan/_process.py	67.06% <0.00%> (-0.12%)	:arrow_down:
qsdsan/processes/_adm1.py	79.42% <71.42%> (-0.84%)	:arrow_down:
qsdsan/processes/_madm1.py	14.64% <14.64%> (ø)

... and 2 files with indirect coverage changes

[yalinli2]

A note that once the disinfection branch in EXPOsan is merged in, the test coverage should be back

[joyxyz1994]

I added a test file for the METAB systems on the EXPOsan@metab branch. Would you like to pull to main for testing?