redacting wifi password

[nikolawhallon]

Related task: https://www.notion.so/redact-passwords-in-wifi-form-17c996f1fe418062b757ccd780811f5d?v=b6ef2b8090d34bb39e788e8eef807c28&source=copy_link

TL;DR the text field when entering the WiFi password is now redacted (could consider extending the virtual keyboard to have this toggle-able?) Some details:

• I don't think Pico8 gives us access to string.rep so I've implemented a tiny helper for redacting text like ****
• I removed some dead comments - happy to re-add if it's useful for the reader, but the Keyboard:new in those comments is using an outdated(?) api
• the settings page has a virtual keyboard which seems only to be used for WiFi - I could have simply had the keyboard constructor take a bool to determine if the text field should be redacted, but instead I decided to update that on the fly, assuming that the settings page could eventually re-use the virtual keyboard for non-sensitive things