Implement I2P integration

[matthias-hoste]

This is a basic I2P integration with I2Pd. I went off of a seemingly abandoned PR(#4263)
Right now after selecting a wallet mode you have the option to use or not use I2P as a tx-proxy.

Left to do for me:

• Advanced mode option to only use I2P(create a tunnel and set an anonymous inbound)
• Add option for pre-existing I2P routers(in case you are running java I2P)
• Add I2P network stats page? Right now it's not even obvious if it's running or what it's doing
• Clean up code, daemon args look very unclean