Reporting for Analytics engine

[abramvandergeest]

Current behavior:
Reporting is only done by explicitly calling a log / sql activity. Makes it difficult to document each step in the process.

Expected behavior:
Add a layer to the base Activity that optionally allows reporting of the activity input/processing/output to an outside source (Log,SQL,SMS,etc.) that could be configured separately (i.e. in its own section of the JSON)

What is the motivation / use case for changing the behavior?
One example is for A/B testing, where it would be good to report input / A/B choice / and result.

Additional information you deem important (e.g. I need this tomorrow):
Does we use "logging activities" plugged into a root level logging key/value in the JSON? Does the logging key have its own builtin logging functions.