[FEATURE] Custom angles for polarArea graph

[MarioIannotta]

Expected Behavior

Provide custom value for each angle of the polar graph.

Current Behavior

Every angle is 360/#values °

Possible Solution

Provide the custom angles in the options like this

 var options = {
 		type: 'polarArea',
 		data: {
 		labels: ["A", "B", "C", "D", "E"],
 		datasets: [{}]
 		},
 		options: {
 			customAngles: [
 				10, 40, 80, 80, 150
 			]
 		}
 	}
 	
 	var ctx = document.getElementById('chartJSContainer').getContext('2d');
 	new Chart(ctx, options);

and use it in

Chart.controllers.polarArea = Chart.DatasetController.extend({...
updateElement: function(arc, index, reset) 

[MarioIannotta]

This should be closed with #4753.

[etimberg]

Possible in v3.0.0-beta.3 https://jsfiddle.net/rbgoeskx/

Will send a PR updating this to use degrees instead of radians