Convert to non-url-safe base64 (everywhere)

[futurechimp]

No description provided.

[futurechimp]

The following annoying binary <--> text encodings in our codebases are Base64-URLSAFE which is inconvenient:

Sphinx

• address encoding, eg in src/route.rs

Nym

Base64 is mostly used for key serialization (Sphinx addresses also exist):

• identity keys
• mixnode keys
• Sphinx address encoding

I quite like @narodnik's idea of using Base58. It won't inflate information space like hex, but you can still read and copy/paste it conveniently and unambiguously.