Fixes bugs in dipolar direct sum on gpu

[RudolfWeeber]

1. Avoid invalid frees
2. Missing Bjerum length (From B.M Tanygin, pull request Rotational motion core fixes: adding mass and dimensionless model related parameters #453
3. Testcase comparing dipolar direct summation methods against each other and checking the scaling with Bjerrum length

[codecov-io]

Current coverage is 27.85%

Merging #456 into master will not affect coverage as of 81d9139

@@            master    #456   diff @@
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  Files          275     275       
  Stmts        65805   65577   -228
  Branches         0       0       
  Methods          0       0       
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- Hit          18331   18269    -62
  Partial          0       0       
+ Missed       47474   47308   -166

Review entire Coverage Diff as of 81d9139

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