Aave v2 migration

[shapeshed]

Upgrades Aave Integration Contract to support a migration to Aave v2.

Assumptions

• The AToken interface will stay the same
• The decimals on AToken will remain the same
• The AToken v2 address will change
• The Aave Platform address may change
• The referral code will stay the same

[alsco77]

A note on the test case - given that they are both fairly similar in setup, it might be cleaner to group the setup into the 'beforeEach' or a 'setup' function that returns the right props. We can also test more properties in each of these test cases..

[alsco77]

I would probably provide less or group unit tests for the arg checking and more for integration tests. For example verifying that checkBalance works correctly after the migration, checking that deposit and withdraw (or swapping) also work correctly after the migration - there should be some cases for that in the file. You could do this all in 1 test case. I think integration tests are most powerful when it comes to these things.

[The-3D]

Please find attached the current interface for ILendingPool V2
ILendingPool.zip