Fix preference restoration for Guru Panel

Preferences.cpp
galaxql.cpp
galaxql.h

(Galaxql::Create)
- Remove setting initial bitmap for mGuruPicture.
This is now handled in ResetGuruPanelToChapter().

(Galaxql::ResetGuruPanelToChapter) New.
- Reset the guru panel widgets mGuruDone, mGuruPicture.
- Select the specified chapter and expose it (show its contents).

(Galaxql::OnGuruDoneClick)
(RestorePreferences)
- Replace code that selects and/or exposes the specified chapter by
calling ResetGuruPanelToChapter().


Prior to these changes preference restoration did not fully reset the
Guru Panel and if it was disabled it would remain so.