documents: use instance variable, instead of the local

(integrated from komodo (trunk) change 81083 by toddw)

git-svn-id: http://svn.openkomodo.com/repos/openkomodo/trunk@13303 b87d16e7-d29f-4ee1-b5ec-817d645d335f
document settings manager: use lazy class attributes, instead of instance properties

git-svn-id: http://svn.openkomodo.com/repos/openkomodo/trunk@13304 b87d16e7-d29f-4ee1-b5ec-817d645d335f