lib/model: Meaningful error messages for paused folders
lib/model: Meaningful error messages for paused folders

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3977
LGTM: AudriusButkevicius, calmh

uok/syncthing,jryans/syncthing,imsodin/syncthing,wweich/syncthing,nrm21/syncthing,jryans/syncthing,le9i0nx/syncthing,syncthing/syncthing,AudriusButkevicius/syncthing,imsodin/syncthing,imsodin/syncthing,lkwg82/syncthing,uok/syncthing,lkwg82/syncthing,jryans/syncthing,xduugu/syncthing,nrm21/syncthing,uok/syncthing,lkwg82/syncthing,wweich/syncthing,rumpelsepp/syncthing,wweich/syncthing,imsodin/syncthing,rumpelsepp/syncthing,le9i0nx/syncthing,lkwg82/syncthing,jryans/syncthing,AudriusButkevicius/syncthing,rumpelsepp/syncthing,syncthing/syncthing,le9i0nx/syncthing,xduugu/syncthing,AudriusButkevicius/syncthing,AudriusButkevicius/syncthing,syncthing/syncthing,syncthing/syncthing,imsodin/syncthing,syncthing/syncthing,rumpelsepp/syncthing,uok/syncthing,le9i0nx/syncthing,nrm21/syncthing,wweich/syncthing,nrm21/syncthing,xduugu/syncthing,syncthing/syncthing,xduugu/syncthing