Echidna tests

[beirao]

Full invariant testing with Echidna on the Reliquary contract.

[beirao]

I tested all these invariants with Echidna:

• A user should never be able to withdraw more than deposited.
• No position.entry should be greater than block.timestamp.
  - The sum of all position.amount should never be greater than total deposit.
• The sum of balances in levels should never be greater than total deposit.
• All arrays defining pools should be equal in size.
• The sum of all allocPoint must be equal to totalAllocpoint.
• The total reward harvested and pending should never be greater than the total emission rate.
• emergencyWithdraw should burn position rewards.
• A position amount should never be greater than the level.balance deposited at the position level.

[beirao]

If anyone has ideas for other invariants, I can implement them quickly. Just send them in English here.