[Proposal] Changing TFI-LP to tfUSD

Original Author: Ryan Rodenbaugh Forum: https://forum.truefi.io/t/changing-tfi-lp-to-tfusd/241

Summary: Change the name of TrueFI LP (TFI-LP) to TrueFi USD (tfUSD) and standardize all future pools around the same format (e.g., TrueFi WETH: tfWETH)

Background: tfUSD is a more explanatory name that will help users feel more comfortable with depositing into the LP-pool and holding the corresponding token. This should also make it easier for other protocols to adopt the token. Additionally, as TrueFi adds more pools over time, it will be good to have a more standard naming convention that can be used by each pool.

Specification: Update name on Etherscan and in all marketing materials.