OpenSystemsDevelopment / qpdf

This is in preparation for restoring a QPDFObject.hh to ease the
transition on qpdf_object_type_e.

This commit was created by
* Renaming QPDFObject.cc and QPDFObject.hh
* Replacing QPDFObject\b with QPDFValueProxy (where \b is word
  boundary)
* Running format-code
* Manually resorting files in libqpdf/CMakeLists.txt
* Manually refilling the comment in QPDF.hh near class Resolver

Move responsibility for creating shared pointers to objects and cloning from QPDFObjectHandle to QPDFObject.

Update getJSON() methods and calls to them

Add virtual methods to QPDFObject, wrappers to QPDFObjectHandle, and
implementations to all the QPDF_Object types.

These object types are to facilitate content stream parsing.