update to the current mupdf core

- update get-mupdf.sh to pull the mupdf code from git, and symlink cmake stuff in the checkout
- look for and use openjpeg (instead of jasper) and jbig2dec
- update the CMakeLists.txt for mupdf sources, with correct sources and removing the (obsolete?) font generation
- update the QMuPDF classes to the new fitz/mupdf pdf code: in general, there is much less code needed now,
although accessing Catalog stuff (like PageMode and the Info dict) requires using the mupdf internals