Memo transaction

Post memo I think on-chain Uber will happen. Here's a rough spec of how it could work: https://github.com/memocash/mips/blob/gigs/mip-0007/mip-0007.md
Reply to memo f6fc1cb8ec4e09ae8d827e26754f7b8144bebd8c292d071d01507a8f2a6f76c4