Add 'refund' api to refund original selling price

[kohlivarun5]

No description provided.

[kohlivarun5]

Might relate to #65.

This should allow seller to refund unused tickets, and close out the contract, for situations like COVID-19.

Seller would need to submit and distribute, maybe clients can fetch refunds from universe or event and burn tickets.

• Needs to ensure client doesn’t take refund but then resell
• Needs to evaluate refunds after resale, probably only original price

[kohlivarun5]

Changes needed:

Solidity

• Remember original sale price per ticket
• Expose total refund amount (view)
• Expose refund tickets (setter)
• Block all resale during refunds (require)
• Expose ticket refunded (view)
• Expose claim refund and burn tickets (setter)

UI

• Get total refund amount
• Allow seller to set refund mode
• Show claim refund instead of use ticket for user
• Allow user to get refund and burn ticket

[MartinRep]

Nice try, man. 😃😃😃