Adding and removing options from live Multiple Choice questions

[lsabor]

See notion document: https://www.notion.so/metaculus/Adding-and-removing-options-from-multiple-choice-questions-1cf6aaf4f101807a87b9d48e35f18956

Scope:

• Add the ability to add or remove options from a live multiple choice question
• Forecasters get abundantly notified well in advance.
• If adding options, standing forecasts are set to expire at the end of the grace period. Users can update during the grace period to override the expiration.
• Scoring should work transparently.

This will serve as the log for the main feature, and will include sub-issues.

sub issues in dependency order:

#3841 add None as valid prediction value
branch: #3842

#3800 add options_history
branch: #3807

#3813 forecasts
branch: #3814

#3806 aggregations
branch: #3818

#3801 scoring
branch: #3809

#3802 notifications
branch: #3826

#3804 updating options
branch: #3827

#3805 graphing & prediction interface
branch: #3828