Display true positive indication in the table

![](https://s3.amazonaws.com/f.cl.ly/items/3K2D2y2Y1d3W3S1L2D1S/Screen%20Shot%202014-12-15%20at%204.56.34%20PM.png)

The way this works:

> This is performed a join on the truth_vcf and the given vcf/run, and added a `tags:validated` attribute to calls which have a corresponding validated call in truth. This is then displayed in the VCF table as a single + to indicate "true positive", with a tooltip displaying on hover.

Fixes #27.

Things TODO, ideally via issues:
* Change indication (unicode checkbox or a NouN Project glyph).
* Allow for sorting/filtering on them (this would include giving the column a header, or figuring something else out for the UI).

Let's wait for #387 to come in and rebase on it before merging this in, since that'll be much easier than the converse.

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