Add Polar chart

[tmecklem]

This PR adds the polar chart type to the chart library, where a polar chart is defined by a chart with polar axes r and t. r represents the radius distance of a point on the chart, and t represents the angular offset from 0 in radians. It also adds the polar chart LiveView Component to the library.

To Do (uncharted core):

• Add polar coordinate system (Chart, Dataset, Axes)
• Add degree units to radians conversion by specifying units: :degrees in axis

To Do (uncharted_phoenix):

• Render points
• Render labels for points
• Render t axis (angular) gridlines
• Render r axis (concentric circles) gridlines