Adding visual captchas for register and login. (#1027)

Adding visual captchas for register and login. (#1027)

* Adding visual captchas for register and login.

* Adding audio wav file for Captcha using espeak.

* Lots of captcha fixes.

- Removed login captchas.
- Added settings to disable captchas, and change difficulty.
- Captchas can only be checked / used once, front end gives a new one on
  failure.
- Added front end button for regenerating captcha.
- Added a disabled / pause button audio playing.

* Some more fixes.