Refactor and renaming of chart data classes

[Brian Lewis]

There is debate around when, in typescript, to use type and when to use interface; but unless there is a need to supply some behaviour, either is better than class.

Also, because there is minimal difference in effect between type and interface drop the Ixxx prefix from those interfaces that have it, like IKeyValuePair

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[Brian Lewis]

task(charts): refactor nd rename some data types

Resolves #906

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