[WIP] Atomic collision model

[jjaraalm]

Working on merging in the atomic collision model. So far it builds, but is untested.

Remaining Items

• [ ] Run a test case with devel
• [ ] Add documentation to wiki
• [ ] Add an example - partially ionized reconnection

[codecov[bot]]

Codecov Report

Merging #135 (421fdf9) into devel (49586ca) will increase coverage by 0.04%. The diff coverage is n/a.

@@            Coverage Diff             @@
##            devel     #135      +/-   ##
==========================================
+ Coverage   83.11%   83.15%   +0.04%     
==========================================
  Files         118      118              
  Lines        7267     7267              
  Branches     1120     1120              
==========================================
+ Hits         6040     6043       +3     
+ Misses        754      752       -2     
+ Partials      473      472       -1     

Impacted Files	Coverage Δ
src/util/pipelines/pipelines_thread.cc	64.48% <0.00%> (+2.80%)	:arrow_up:

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