Allow importing contracts inside test suites

[fubuloubu]

Overview

Brownie provides contract types as fixtures, however it would be helpful to also allow importing them via from brownie import ContractType, then you could do useful stuff like this:

import pytest
from brownie import ProtocolV1, ProtocolV2

@pytest.fixture(params=[ProtocolV1, ProtocolV2])
def protocol(accounts, request):
    yield accounts[0].deploy(request.param)

This would parametrize the fixture such that it would run any tests it touches twice, once with ProtocolV1, and once with ProtocolV2.

[iamdefinitelyahuman]

This does work in tests, but not in conftest.py apparently. Shouldn't be a hard fix, just need to ensure the project is loaded before plugin collection happens.