refactor expression code in Param constructors

[berndbischl]

this is really badly cluttered copy-paste stuff from @kerschke
many code blocks are repeated dozen times

basically I mean this here

  ## makeIntegerVectorParam is not able to use expressions in 'length', thus we
  ## do a dirty-hack, in which we define len = 1L for the construction of p and
  ## afterwards re-insert the expression for the length
  len.expr = NULL
  if (is.expression(len)) {
    len.expr = len
    len = 1L
  } else {
    len = asInt(len, na.ok = TRUE)
  }
  if (is.na(len))
    p = makeVectorParamNALength(makeIntegerVectorParam, default = default,
      id = id, lower = lower, upper = upper, requires = requires, tunable = tunable, special.vals = special.vals)
  else
    p = makeIntegerVectorParam(id, len = len, lower = lower, upper = upper, default = default,
      requires = requires, tunable = tunable, special.vals = special.vals)
  p = learnerParamFromParam(p, when)
  ## re-insert the expression (if it existed in the beginning)
  if (!is.null(len.expr))
    p$len = len.expr
  else
    p$len = len
  return(p)

[berndbischl]

@mllg done....