JSON doesn't support functions which are needed to create scriptable options, so implement a very basic method to load a JavaScript file exporting the config in `module.exports`. Also rename test sources (remove the `jasmine.` prefix), cleanup `karma.conf.js` and add an example .js fixture config (bubble radius option).
* 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"
`karma.conf.ci.js` has been merged into `karma.conf.js` for local testing consistency: `gulp unittestWatch` has been replaced by `gulp unittest --watch` and thus use exactly the same config file. Upgrade to latest jasmine and karma packages and remove deprecated `gulp-karma` dependency (directly use `karma.Server` in gulp).
Split `test/mockContext.js` into smaller `test/jasmine.*` modules to make easier unit tests maintenance and finally, move all `*.test.js` files under the `test/specs` folder.
