Other entities proposed to extend pivot and other functionality

[ianhelle]

We can use additional entities to hang pivot and other operations from.
Examples:

• process_id
• user_agent

Which entities make sense to add?
Do we need full-fat entities (classes) or can we create lightweight classes (maybe dynamically) to host these properties.

Some related thoughts;

• we could accept entities in place of their string representation (process, ip address)

• entity collections?

• if we're returning stuff as dataframe, how can we easily extract the desired items (and pass them to futther functionality)

• chat more to Mark @aeetos about this.