* added 'angle' option to polar charts. image comparison test is work in progress; not currently passing
* removed unnecessary variable assignment
* code cleanup based on PR; for 'angle' option on polarCharts
* Made polar chart image comparison test pass by removing debug flag. Also explicitly marked _computeAngle as private.
* Removed visibleCount computation in polar chart
* split out code related to updating the radius in polar chart's update function, into it's own 'updateRadius' function
* made updateRadius method private
* fix linting error
* updated polar charts to read custom angles from "chart.options.elements.arc.angle" instead of "chart.options.angle"
