Added quartile_int to `Direct elicitation in 1D

[rohanbabbar04]

Solves #289

Description

• Added quartile_int example to Direct elicitation in 1D.
• Also added a quartile_int.gif if the user cannot run the previous cell(similar to roulette).
• Added it separately below roulette

Checklist

• Code style is correct (follows pylint and black guidelines)
• Includes new or updated tests to cover the new feature
• New features are properly documented (with an example if appropriate)
• Includes a sample plot to visually illustrate the changes (only for plot-related functions)
• Widget states have been properly saved (only for notebooks with widgets) see for details.

[aloctavodia]

Thanks @rohanbabbar04