Implement Delete

[ed255]

How hard will it be to implement a Delete function in the Tree?
This feature would be useful in vocdoni-node in the StateDB, where the Tree is a collection and sometimes we want to remove entries (for example, the list of oracles, or the list of validators).

[arnaucube]

Not quite hard, similar to Update or Add but with few differences for the logic when going up from the leaf. I understand that for the use case is not urgent for next week couple of weeks, it can be done once we finish the current iteration ^^