Add add/remove Curve liquidity mini-app

[gabmontes]

Create a mini-app to add & remove liquidity to/from Curve metapools.

[jgarzik]

This is an add-with-fees and remove-with-fees type operation.

• User story: Query metapool address from user. Use address to derive which tokens are in the metapool. We only support cases where the derived answer is: unknown-token + 3pool (i.e. 3pool is 1/2 of the pair)
• User story: When depositing, display user's 3pool and deposit-token wallet balances.
• User story: When withdrawing, display user's inside-pool pair balances.
• User story: Multiple token deposit. Two numeric input fields, one for each token in the token pair. User may choose to deposit any amount of 3pool LP tokens and/or deposit-tokens (ie. VUSD).
• User story: Multiple token withdraw: User may choose to nnnn.nn amount of LP tokens to burn, receiving the underlying 3pool LP tokens + deposit-tokens.