"https://devnet.thetangle.org" is no longer supported

[huggre]

"https://devnet.thetangle.org" is no longer a valid URL
I suggest we use "https://utils.iota.org/....../devnet" instead.

"https://devnet.thetangle.org" is referenced in the following examples:

e02_send_hello.py
e06_send_tokens.py