Fixed definition of allocation and utilization for drones

[rcaspart]

This pull request addresses the wrong definition of allocation and utilization for the drones reported in #87 . The calculations are set to mirror the definition used in COBalD.

Closes #87

[codecov]

Codecov Report

Merging #94 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #94   +/-   ##
=======================================
  Coverage   59.89%   59.89%           
=======================================
  Files          15       15           
  Lines         763      763           
  Branches      111      111           
=======================================
  Hits          457      457           
  Misses        282      282           
  Partials       24       24           

Impacted Files	Coverage Δ
lapis/drone.py	74.50% <ø> (ø)

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[eileen-kuehn]

Hi @rcaspart, thanks for your contribution :) I will have a look after I made a release for the thesis of Tabea.