Feature/lixin/gp from aimd

[nw13slx]

Slight modification and clean up for gp_from_aimd module and output module

• min_atoms_added function enable. training is only called when added atoms are more than this parameter
• hyper parameters printing is more formatted in gp_from_aimd and gp_algrebra
• output.py is cleaned up. replacing all the string format into f-string.

[codecov-io]

Codecov Report

Merging #88 into master will increase coverage by 0.27%.
The diff coverage is 84.61%.

@@            Coverage Diff             @@
##           master      #88      +/-   ##
==========================================
+ Coverage    41.3%   41.57%   +0.27%     
==========================================
  Files          29       29              
  Lines        4966     4998      +32     
==========================================
+ Hits         2051     2078      +27     
- Misses       2915     2920       +5

Impacted Files	Coverage Δ
flare/gp_algebra.py	59.06% <50%> (-0.04%)	⬇️
flare/gp_from_aimd.py	85.21% <72.97%> (-2.51%)	⬇️
flare/output.py	95.1% <94.23%> (+0.25%)	⬆️

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[stevetorr]

Looks great! I'm curious to hear your 2 cents on the hyperparameter labels but besides that feel free to pull.