MSA Client ID has been moved to CMakeLists.txt, and defaults to the
Client ID for the PolyMC application.
Removed secrets/notsecrets library, replace with (temporary?)
program_info subdirectory.
Support URLs (bug tracker, Discord guild, subreddit) are now specified
as cache variables in cmake, and the buttons are not shown if no value
is set for them.
This is an early-stage move towards debranding the MultiMC codebase,
and will (hopefully) alleviate support requests coming to us from
illicit forks.