Photon implementation

[tbruyelle]

From the AtomOne Constitution Article 3 Section 5

Section 5: The PHOTON Token
The PHOTON shall be the only fee token except for ATONE to PHOTON burn transactions. This applies for all transactions on the root and core shards, and all IBC and ICS payments.

ATONE tokens may be burned to PHOTON tokens at a conversion rate set by law such that the total amount of PHOTONs mintable through burning ATONE tokens shall be capped at 1B PHOTON tokens.

PHOTONs cannot be converted back into ATONE tokens.

The implementation work will be splitted in multiple tasks, each possibly involving a different PR:

• The photon ADR (docs: ADR-002 The Photon Token #34)
• The photon mint message (feat(x/photon): mint photon message #53)
• The photon ante decorator (feat(x/photon): validate fee ante decorator #54)
• The photon denom metadata migration (feat(x/photon): migration #55)
• Documentation about validator config and minimum-gas-price (docs: v2 upgrading instructions #51)