Laboratory Support for Protocol 18

[shanzzam]

As part of the upcoming Protocol 18 changes, we'll want to address the following in the Laboratory code:

• Support the CAP-38 operations LiquidityPoolDepositOp and LiquidityPoolWithdrawOp
• Add new endpoint support for Liquidity Pools
• Update ChangeTrust Operation (see Update with CAP-38 operations js-stellar-sdk#692)

Details can be found in stellar/js-stellar-sdk#693
This work would ideally be done as close to testnet reset as possible.