Allow namespace collision between interfaces

[iamdefinitelyahuman]

What I did

Lessen the namespace collision restrictions.

Closes #729

How I did it

When looking for collisions, allow multiple uses of the same name so long as only one of the objects is a contract. This way projects using interfaces with the same name as the actual contract will now compile.

How to verify it

Try to compile https://github.com/compound-finance/compound-protocol using Brownie

[priyankaj1910]

I am getting this error - NamespaceCollision: Multiple contracts or interfaces with the same name
SimpleStorage: contracts/arbitrum/SimpleStorage.sol, contracts/ethereum/SimpleStorage.sol

I checked the network list .but there is nothing duplicated. It was working fine, but when I added one network and deleted that after that brownie compile stopped working with this error

Can any one please help. I have tried un installing python and brownie and reinstalling, but same error