This fixes the potential edge case where a frozen then unfrozen qTox instance could have its locks delete by a new qTox instance.
We now check that we still own our locks, restoring them if we can, before saving
Starting a new instance with the -p option will force it to start a new instance with the given profile instead of bringing an eventual existing instance to the foreground
Two instances can not run with the same profiles, the profile locking code will ensure that. A user who likes to live dangerously could manually delete the lock to force two instances on the same profile, but such an hypothetical user would be asking for it.
If a qTox instance starts and becomes owner of the IPC shared memory on its first try, it considers itself the only running freshly-started instance, and deletes any possibly stale lock before starting up. This should be fine in the vast majority of cases, but if an existing qTox instance freezes for a long enough time to lose ownership of the IPC and a new instance is started without first killing the frozen one, the frozen instance's lock will be deleted as stale by the new one. If the frozen instance subsequentely unfreezes, it will be running on a profile for which it doesn't have a lock, which could cause trouble. This is an intentionaly allowed edge case, the alternative being a stale lock staying forever until removed manually. A potential solution not yet implemented would be to check that the lock is still actually present before attempting any write.
