Cleanup multiblock code

[jipolanco]

No description provided.

[codecov-commenter]

Codecov Report

Merging #93 (a146169) into master (2dfb842) will increase coverage by 1.55%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #93      +/-   ##
==========================================
+ Coverage   93.90%   95.45%   +1.55%     
==========================================
  Files          16       16              
  Lines         787      770      -17     
==========================================
- Hits          739      735       -4     
+ Misses         48       35      -13     

Impacted Files	Coverage Δ
src/WriteVTK.jl	85.71% <100.00%> (+1.50%)	⬆️
src/gridtypes/multiblock.jl	98.52% <100.00%> (+14.25%)	⬆️

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