PATCH: Save & restore last active panel in Options dialogue

Hello All,

This little improvement saves some time for a user actively playing
with program's options. Last chosen treeview item label (translated!)
is saved among other settings and used on next dialogue invocation to
find and select treeview item with same label.

Сontrol over panels visibility moved to a single function
frmOptions::ShowPanel(menuItem), making future modifications a bit
easier. By the way, a call
pnlDatabaseDesigner->Show(false);
was missing in frmOptions constructor.

Also it seems that empty panel is of no use when selecting
parent-level items like "Browser" or "Query tool". I'd suggest to
show panels corresponding to their first children, like "Display" or
"Query editor".

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Best regards,
Vadim