SettingsAccessor: Keep version information in map up to date

Introduce a original version to indicate which version the map was
upgraded from.

THIS CHANGE REMOVES SUPPORT FOR .USER FILES WITHOUT VERSION INFORMATION!

Those files were written before Qt Creator version 1.3.

Change-Id: I2c7264cf84c458b139a9073fc415c257dfbd0498
Reviewed-by: Daniel Teske <daniel.teske@digia.com>