As the faucet will always ask for a captcha now, the current script is
no longer usable.
Change the script to print the captcha in dot-matrix to the terminal,
using unicode Braille characters.
Currently, using the getcoins.py with a custom signet executes successfully and shows the transaction as complete, however for obvious reasons, it should not.
This PR adds a sanity check for custom signet by comparing the current network's first block hash with global signet's respective hash.
