Default to %ProgramData%\obs-studio\plugins\ on fresh installs.
Restore the previously recorded install path on upgrades, so users
who installed to a custom location are not silently moved.
Don't reuse the old installation dir since it might not be compatible
with the new layout.
Ensure previous legacy install is cleaned up to avoid plugin being
installed twice.
Based on OBS plugin template build scripts with some minor adjustments:
* Adjust format check scripts to exclude ./deps folder
* Adjust release scripts to only draft releases
* Always build installers
* Always upload build artefacts
* Build opencv for Mac and Windows releases
