Add flag for auto-validation

[connorjayr]

Is your feature request related to a problem? Please describe.
The auto-validation feature can be distracting and sometimes laggy for larger truth trees, especially on slower computers or older browsers.

Describe the solution you'd like
The user should have an option to turn off auto-validation; if turned off, the user would then validate the truth tree by pressing a button, perhaps in a dropdown menu.

Describe alternatives you've considered
This feature would be best implemented as a simple option, so no alternatives have been considered.

Additional context
There is no additional context.

[connorjayr]

Closing as this is likely not needed anymore, since the validator has been re-written and is much faster than when this issue was opened.