Replace httpserver-b64decode.lua with encoder module

[marcoskirsch]

We use Base64 decoding in the implementation of Basic HTTP Authentication.

NodeMCU provides Base64 decoding through the encoder module

We should get rid of httpserver-b64decode.lua (too bad, at the time it was a pain in the ass to get it to work on NodeMCU's extreme memory constraints) and instead make the encoder module a requirement for HTTP Authentication. It should be much faster and use less memory.