After loading SettingsSerializer would keep the last group/array as current, so setting new values before the next beginGroup/beginWriteArray would be added to this group/array wrongly
This has zero inpact on qTox since we don't load before saving
We now use a binary serialized format to save space and allow clean encryption of the user settings.
All the settings can (and should) be edited from the GUI so there is no loss of functionnality.
It can still read the old .ini format, and will seamlessly upgrade to the new format.
Fixes#1810
