Rename abstract type pool to Pool

[CasBex]

Closes #425

[codecov[bot]]

Codecov Report

Merging #426 (2afb095) into master (cdce9eb) will not change coverage. The diff coverage is 66.66%.

@@           Coverage Diff           @@
##           master     #426   +/-   ##
=======================================
  Coverage   74.36%   74.36%           
=======================================
  Files         147      147           
  Lines        8132     8132           
=======================================
  Hits         6047     6047           
  Misses       2085     2085           

Impacted Files	Coverage Δ
...c/RL/utils/geometricflux/heterogeneousgraphconv.jl	0.00% <0.00%> (ø)
src/RL/utils/geometricflux/geometricflux.jl	100.00% <100.00%> (ø)
src/RL/utils/geometricflux/graphconv.jl	30.23% <100.00%> (ø)

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[jardinetsouffleton]

Thank you very much @CasBex !!