PluginManager: Refactor loading plugins

- Auto enable all plugins in the base folder, this allows package
maintainers to ship plugins

- Give plugins in the user folder priority over plugins in the base
folder
3 jobs for master in 5 minutes and 35 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #17604
run-appdata

00:00:06

passed #17603
run-tests

00:05:17

 
  Build
passed #17605
run-build

00:00:11