Add optional calculator input to ase otf constructor

[jonpvandermause]

Summary

• Allows an ase calculator to be given as input to the ase otf constructor. This makes it possible to avoid a deepcopy in the from_ase_atoms method, which is needed for non-picklable C++ calculators
• Removes a duplicate method in ase otf

[codecov-io]

Codecov Report

Merging #271 (2629f3f) into development (d2d0900) will not change coverage.
The diff coverage is 50.00%.

@@             Coverage Diff              @@
##           development     #271   +/-   ##
============================================
  Coverage        54.87%   54.87%           
============================================
  Files               51       51           
  Lines            11925    11925           
============================================
  Hits              6544     6544           
  Misses            5381     5381           

Impacted Files	Coverage Δ
flare/ase/otf.py	87.75% <50.00%> (ø)

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