Masked Somatic Mutation Track

[agduncan94]

Overview
Data Format - MAF
Data Category - Simple Nucleotide Variation
Data Type - Masked Somatic Mutation
Example File ID - 27f42413-6d8f-401f-9d07-d019def8939e

Notes
Add a SeqFeature for Masked Somatic Mutation Track. This is a MAF. This is an aggregated version of a VCF file, so investigate if they are actually the same format. It may be that we can reuse the store classes for VCF files.

Investigate the best way to display tracks (XYPlot vs HTMLFeature).

[agduncan94]

Related to #81