OP-781: initial commit for slow Option Dialog creation fix; fix consists
in lazilly creating option pages when user selects them instead of
creating them all upfront. Dummy placeholder widget (QLabel) are initially
created instead of the real option page; this commit also fixes a minor
issue where the left tree selection would not be in sync with the
displayed option page (see Jira for more details).
OP-781: cleaned up; added comments; removed some debug code; fixed tabs
into spaces
OP-781: reorganized imports
Merge pull request #169 from PhoenixPilot/kenz/OP-781

Speed up opening the preferences pane - op 781