Correctly preload settings
(#21)
Don't check enabled state from ps.loadSettings*()
+ remove SETS_LOAD_SKIPPED flag
We don't want to load prefSvc.js in disabled mode and do all checks before call ps.loadSettings*()
(related to #21)
Remove obsolete ps.SETS_LOAD_EVAL_ERROR flag
Preload settings only once
(#21)