Further updates to buzzer, keypad, and ssd1306

[Tails86]

For Buzzer:

• Instead of spawning off a bunch of threads to buzz, do all the work in a single thread

For Keypad:

• Separated "cancel" from "error" beeps
• Fixed bug when floating point number entered in settings page would not be applied (previously, only integers were accepted)

For SSD1306:

• Added help page to describe how to setup hardware/software for this plugin
• Refactored to separate screen text processing from hardware handling
• Updated signals to this plugin so another plugin may completely take control of the display if they would like
• Added unit and component testing for this plugin so that it may be tested without hardware attached
  • This may be executed on Windows or from Raspberry Pi. SIP and smbus are stubbed out, so only the plugin directory itself is needed to run.