Adds support for building Lokinet as a system extension, and fixes
various problems in the macos implementation found during development of
the system extension support.
CMake will set version variables itself if you give the version in the
project(), which is cleaner. Also removes some (nearly) duplicate
definitions and settings added in basic_definitions.cmake for unknown
reasons.
Removes some redundant settings (name, description, version) from the
cpack settings which already default to the values from the project()
call.