Grid flood fill

[SimonEnsemble]

@Surluson here is my implementation of the flood fill algo, segmentation, and blocking of inaccessible pockets. some tests were added to grid_tests.jl and henry_tests.jl

[coveralls]

Pull Request Test Coverage Report for Build 210

• 81 of 85 (95.29%) changed or added relevant lines in 2 files are covered.
• 7 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.2%) to 87.579%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/Grid.jl	80	84	95.24%
<!--	Total:	81	85	95.29%	-->

Files with Coverage Reduction	New Missed Lines	%
src/Grid.jl	7	91.37%
<!--	Total:	7		-->

Totals
Change from base Build 187:	0.2%
Covered Lines:	832
Relevant Lines:	950

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💛 - Coveralls

[SimonEnsemble]

thanks @Surluson. fixed. the default value for energy_tol is sort of subjective and depends on how rigorously you want to exclude MOFs that have some sort of diffusion limitation. I think 10 kT is a good default for the energy that is considered a barrier. e.g. 15 kT was used here, but there is not a rigorous justification of it to my knowledge.