Tab hierarchies not preserved with OneTab

[TempSpas]

I'm not sure if this is a bug inherent to OneTab, or if it's due to Tab Tree not making available any sort of tab hierarchy for use by other extensions. As it stands, currently when using OneTab to store a browsing session for later use, restoring the session completely destroys the hierarchy of the session using Tab Tree.

[dark-saber]

OneTab destroyed the tab hierarchy with Tree Style Tab too, by the way. I wonder if there's any standard hierarchy API to work with other addons.

[polyzen]

Duplicate of #192.