Improve metadata visualization

[JDTheRipperPC]

Resolves #151

• Added background color
• Added spacing to the arrow labels
• Added box with extra information below the fields
• Changed arrow style to "crow"

[codecov-io]

Codecov Report

Merging #153 into master will increase coverage by 2.89%.
The diff coverage is 94.44%.

@@            Coverage Diff             @@
##           master     #153      +/-   ##
==========================================
+ Coverage   87.96%   90.85%   +2.89%     
==========================================
  Files          12       12              
  Lines         864      886      +22     
==========================================
+ Hits          760      805      +45     
+ Misses        104       81      -23

Impacted Files	Coverage Δ
sdv/metadata.py	89.56% <94.44%> (+7.39%)	⬆️

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