simplify param scoping and centralize dependencies

CMakeLists.txt

Makefile

src/modules/systemlib/param/CMakeLists.txt

src/modules/systemlib/param/parameters_injected.xml

src/modules/systemlib/param/px4params/README.md

src/modules/systemlib/param/px4params/__init__.py

src/modules/systemlib/param/px4params/dokuwikiout.py

src/modules/systemlib/param/px4params/dokuwikirpc.py

src/modules/systemlib/param/px4params/markdownout.py

src/modules/systemlib/param/px4params/scope.py

src/modules/systemlib/param/px4params/srcparser.py

src/modules/systemlib/param/px4params/srcscanner.py

src/modules/systemlib/param/px4params/xmlout.py

src/modules/systemlib/param/px_process_params.py