Scaled UI reference implementation

Follows the Scaled UI TEP (not yet merged).

Based on the Jetton with Governance. Please also check the base project's readme.

Differences from the base project

This implementation differs from the base project in that it implements the Scaled UI TEP (specifically, the get_display_multiplier get method, as well as a display_multiplier_changed#ac392598 event when the return values of that get method change), and also another feature to help with the administration of the contract, particularly, the ability to schedule a change of the display multiplier at a certain timestamp, as well as a permissionless operation to enact said change when the time comes.

The deployment script is changed to:

1. Use USDT wallet code (without compilation; builds library cell)
2. Emit a display_multiplier_changed upon initialization in accordance with the TEP