Bug fixes

• Adjust behavior of "positive" arg for classif.logreg (#2846)

• Consistent naming for dummy feature encoding of variables with different levels count (#2847)

• Remove {nodeHarvest} learners (#2841)

• Remove {rknn} learner (#2842)

• Remove all {DiscriMiner} learners (#2840)

• Remove {extraTrees} learner (#2839)

• Remove depcrecated {rrlda} learner

• Resolve some {ggplot2} deprecation warnings

• Fixed information.gain filter calculation.
  Before, chi.squared was calculated even though information.gain was requested due to a glitch in the filter naming (#2816, @jokokojote)

• Make helpLearnerParam()'s HTML parsing more robust (#2843)

• Add HTML5 support for help pages