New feature: Compute

[ashwin100196]

This feature would involve creating a new column from existing ones. Support for formulas like the excel formula bar would be the expected functionality.

Example

A**2
A + B / C
A == C
A = 0

Target column name would also need to be provided here, which can be a new column or an existing one.

I would like to start contributing from this feature, will generate a pull request once complete. Any thoughts?

[schlerp]

Sounds great, this is indeed the next feature I was looking at implementing. This would require a robust way of nodes knowing what the columns of their predecessors are and i had toyed with a couple of different ways. Currently its handled in the flow object in flows.py but feel free to try out different ways of passing it around. I was also thinking this might be a good choice to use neo4j for handling this? I look forward to seeing your pull request!