fix style, explode, allowReserved defaults for parameter and encoding objects

- explode defaults were wrong for encoding object
- allowReserved defaults were wrong for encoding object

in parameter objects:
- explode: always false for "in: path", "in: header"
- explode: always true for "in: cookie" ("style: form" is the only option, and
  defaults to "explode: true")
- explode: only true for "in: query" when "style: form" (the default style for
  this location)

in encoding objects:
- style: default is "form", but only when "explode" or "allowReserved" are present
- explode: default is true when "style: form" (the default style) and otherwise
  false, and not included at all unless "style" or "allowReserved" are present
- allowReserved: default is false, but only when "style" or "explode" are present

that is: when none of style, explode or allowReserved are present, "contentType"
is used (or a default is calculated), so none of style, explode or allowReserved
shall have default values