Adds freeze_all_dihedrals option

[AlexHeide]

I've been experiencing some git history issues where commits from image_rfo have been getting duplicated and show up as 'n' extra commits. I'm not sure if this is an issue with a squash or rebase performed on that branch. This commit was manually extracted from another, larger PR.

[psi-rking]

Sorry. It could well be my fault for trying a rebase on the other branch, but I haven't done anything strange now for many days. I'll not make that mistake again. You are seeing prior commits dropped?

[codecov]

Codecov Report

Attention: Patch coverage is 85.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 83.06%. Comparing base (db3eb00) to head (f6edbed).
Report is 1 commits behind head on master.

Files	Patch %	Lines
optking/addIntcos.py	82.35%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #99      +/-   ##
==========================================
+ Coverage   83.02%   83.06%   +0.03%     
==========================================
  Files          35       35              
  Lines        7059     7079      +20     
==========================================
+ Hits         5861     5880      +19     
- Misses       1198     1199       +1     

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[AlexHeide]

They're not being dropped, I'm seeing commits that should have been included in previous PRs already getting duplicated and being listed again in the history. I may have been misusing the --track feature and after some rebasing the history is just messed up, but I've resorted to just extracting the actual commit I want and starting from a fresh branch that tracks psi-rking/master.

[AlexHeide]

Ready for review. Once you fully approve, I need to get 0.3.1 out.