Added the k nearest neighbors trend detection algo to the build.sbt 

Note that I removed two type arguments in the KnnTrend.scala file. With this builder, it complains about group's function "sum". Compiler says that _.sum does not takes any type argument. But actually it should. Expect some error at the execution because of that.

also looks like some extra white spaces were removed by the sbt build. I'm including the change so it won't show up anymore.

Algo the algo will still not work as is. Some config still need to be done with sbt. This does not affect anything else.
Merge branch 'trending_algo' of https://github.com/pikaille/PredictionIO into trending_algo