Add page regarding Aggregation

[lcjohnso]

Wanted: high-level summary of aggregation tools, focusing primarily on panoptes_aggregation Python package.

Aggregation Specifics

• Current Aggregation software docs: https://aggregation-caesar.zooniverse.org/docs
• Aggregation launch blog: https://blog.zooniverse.org/tag/data-aggregation/
• Point to Jupyter notebooks (or wait for new versions)?
• Possibly Useful: Cliff's Agg Slidedeck

Other Resources

• https://github.com/zooniverse/Data-digging