Smart contract which uses [AvlTreeMap]s to give nicknames to addresses.
The use of [AvlTreeMap]s allows for much larger contract state as it is not serialized when given to the wasm runtime.
Gas cost is therefore independent on the size of the [AvlTreeMap].
Note: [AvlTreeMap] operations do not create a new state that must be returned. Instead, it updates the underlying map
in mutable manner. If an actions fails the changes to an AvlTreeMap are still rolled back.