fix: split default/optional/required option declarations

inheriting required options cannot be unrequired otherwise and would
fail for some, eg. DocumentImageOptions that have the width/height
attribute optional instead of required like the base ImageOptions class.
remove dead files

outdated, not used, dead code
fix(filter): process multiple output files in chain filter
fix(filter): use tmpfs for php imagine filters
fix(filter): accept text files in unoconv convert