Implementing rollback in revertbot and rollbacktoken in revision class

Added option of -rollback which allows rollbacking instead of simple reverting,
This can be useful in cases like Wikidata or Flow boards.

In order to make this happen I had to add rollbacktoken as a property of revision

Change-Id: I78d4181878cce00fd65194f2a3b12f57cd096977
Merge "Implementing rollback in revertbot and rollbacktoken in revision class"