Security audit for opium protocol v2

https://forum.opium.network/t/proposal-security-audit-for-opium-protocol-v2-smart-contracts/387

Providing security audit for Opium protocol v2 by Igor Gulamov.

Scope of the audit: https://github.com/OpiumProtocol/opium-protocol-v2/tree/24b2d653bade302d522a5b588595e9728f6f9995

contracts/core/Core.sol contracts/core/OpiumProxyFactory.sol contracts/core/OpiumPositionToken.sol contracts/core/OracleAggregator.sol contracts/core/TokenSpender.sol contracts/core/SyntheticAggregator.sol contracts/core/registry/Registry.sol contracts/core/base/RegistryManager.sol