Plot frequencies as pie charts on a map

[alimanfoo]

Add a function to plot a map with pie charts overlaid showing frequencies within cohorts.

This is an umbrella issue, covering several related use cases but that all could re-use some common code for plotting pie charts on a map.

Use case 1 - Plotting taxon frequencies.

Pie charts of taxon frequencies.

Use case 2 - Plotting gene CNV frequencies.

Pie charts of copy number frequencies.

Use case 3 - Plotting inversion karyotype frequencies.

(Plot created by @sanjaynagi.)

Use case 4 - Plotting SNP allele frequencies

Something similar to CNV or karyotype frequencies, but for a single SNP.

[alimanfoo]

@ahernank, could you post a link to the code you used to plot the Senegal taxon and CNV pie charts?

[alimanfoo]

Here's @sanjaynagi's karyotype frequency map code.