Fixes issues with conversions to CategoryDataset

- most importantly series and category were inverted, this is now fixed,
  so it works like this:

    val data = List (
      "Series 1" -> List("bin1" -> 1, "bin2" -> 2),
      "Series 2" -> List("bin1" -> 3, "bin2" -> 4)
    )

    data.toCategoryDataset

- for the same inversion issue the conversions from Coll[(A,B)] to
  CategoryDataset has been modified to
  - the values of type A now specify the categories / bins
  - the series name comes from the parameter list

- all conversions that return a single series or a wrapper of a single
  series now provide to name that series, scaladoc reflects so in use
  cases