session.conf split follow-up: plugins (PR #3183)
Move plugin layout to session.conf
The plugin related settings can be considered session data. They
encode local paths that wouldn't work on other machines. Also I would
say it's not unusual to have a different set of plugins enabled on a
different machine.
The "load_pluings" key is moved as well to keep things simple. No
idea what's the use case to set this off. Typically you just have no
plugins enabled and the debugging aid `geany -p` bypasses any of this
anyway.