ChartsWidget and ChartWidget to unify layout building and better typed methods to clarify parameters

[tumaysem]

ChartsWidget and ChartWidget to unify layout building and better typed methods to clarify parameters

fixes #16

[coveralls]

Pull Request Test Coverage Report for Build 3839885148

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 59.571%

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Totals
Change from base Build 3821613699:	0.0%
Covered Lines:	333
Relevant Lines:	559

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💛 - Coveralls

[anirudh2]

@aasseman Are you good? If so, please approve, so that the merge isn't blocked.

@tumaysem Could you rebase to master?