REX: buying REX immediately moves to REX savings

[DenisCarriere]

Purpose

When buying REX, immediately send received REX to savings (locked until user request to unstake).

buyrex automatically sends rex_received to mvtosavings.

Feedback provided by

• @DenisCarriere
• @nsjames

Code example

mvtosavings( from, rex_received );

Preconditions

• mvtosavings whenever buyrex is called by user

References

• rex_received
• mvtosavings

Note: changes should be pushed to Antelope Reference contracts https://github.com/AntelopeIO/reference-contracts

[DenisCarriere]

Implemented via AntelopeIO/reference-contracts@6d791ad

Additional unit tests is required