Add t and z stats to edgeR/qlf results from calculateIndividualLogFC

[This is the way](https://support.bioconductor.org/p/120780/#120785)

```r
t.stat <- sign(qlf$table$logFC) * sqrt(qlf$table$F)
z <- zscoreT(t.stat, df=qlf$df.total)
```