Add additional context to Action Settings Documentation

[shua123]

It would be great to get additional context for the "action settings" options.

Examples:

1. For "replace", what is that actually doing? On http://socrata.github.io/datasync/resources/control-config.html#actions it says "DataSync will calculate the minimal set of changes required, updating the dataset accordingly" though explanations on other pages like http://socrata.github.io/datasync/guides/setup-standard-job.html and the app tool-tip do not say this.
2. What are the pros, cons, and best practices for each option?
3. How does each option affect metadata fields like viewLastModified and rowsUpdatedAt as well as the record level "System Fields" described at https://dev.socrata.com/docs/system-fields.html? Provide example details for common scenarios.