Remove java interface convention

[jjatie]

All protocols prefaced with "I" have been renamed with the "I", following Swift API guidelines.
The concept of Interfaces were carried over from the Java implementation and don't belong here.
All DataSet "Interfaces" have been removed as they don't provide anything to the framework that subclassing doesn't already provide. This also makes DataSets like other related types including ChartData, DataEntries, ChartViews, etc.

[codecov-io]

Codecov Report

Merging #2795 into master will increase coverage by <.01%.
The diff coverage is 24.48%.

@@            Coverage Diff             @@
##           master    #2795      +/-   ##
==========================================
+ Coverage   19.64%   19.64%   +<.01%     
==========================================
  Files         113      113              
  Lines       13792    13791       -1     
==========================================
  Hits         2709     2709              
+ Misses      11083    11082       -1

Impacted Files	Coverage Δ
...Renderers/BarLineScatterCandleBubbleRenderer.swift	54.83% <ø> (ø)	⬆️
.../Implementations/Standard/BubbleChartDataSet.swift	0% <ø> (ø)	⬆️
...Charts/Renderers/Scatter/CircleShapeRenderer.swift	0% <ø> (ø)	⬆️
...plementations/Standard/LineRadarChartDataSet.swift	16.66% <ø> (ø)	⬆️
...rts/Renderers/LineScatterCandleRadarRenderer.swift	9.09% <ø> (ø)	⬆️
.../Implementations/Standard/CandleChartDataSet.swift	0% <ø> (ø)	⬆️
...ource/Charts/Formatters/DefaultFillFormatter.swift	5% <ø> (ø)	⬆️
...ce/Charts/Formatters/IndexAxisValueFormatter.swift	0% <ø> (ø)	⬆️
...ata/Implementations/Standard/PieChartDataSet.swift	0% <ø> (ø)	⬆️
...ata/Implementations/Standard/BarChartDataSet.swift	57.74% <ø> (ø)	⬆️
... and 54 more

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