ranger should be refactored

[mb706]

There seem to be a few issues in the paramset of ranger

• "alpha" is present in classif and regr, but according to ranger docs this is only valid for 'maxstat' splitrule, which exists only for survival? Also the case for 'minprop' and likely for some others.
• 'lower' of max.depth should be '1', not '0'. '0' is a special value, same as NULL, which has different behaviour from other values. Having 0 as part of the non-special-value-range confuses optimizers
• default of 'respect.unordered.factors' should not be 'ignore', it should not be set (since the default depends on what value 'splitrule' has)

Someone should probably read over this and check for other issues as well.