Modification to EM algorithm

See pull request #49
Changes were made to the m method in Quantify.scala so that the
"quantify unique transcripts" sparkTest in QuantifySuite.scala
passes. The problem was that in the m step of the EM algorithm,
the weight of equivalence class j for transcript i alpha_ji has
to be multiplied by the fraction of k-mers in equivalence class j.
The Sailfish paper (Patro et al., 2014) does not include this
in the EM algorithm equations it provides in the methods section.
It'd be better to do:

```
equivalenceClassCounts.map(kv => kv._2).reduce(_ + _)
```

IMO. It'll be more performant to do the reduce on `Long`s instead of on a `Tuple2`.