Update Result Calculations for Facebook Ads

This MR:

1. Removes the conversion calculations from results from all Ads Insights base models
2. Removes the actions_conversions calculated metric from all Ads Insights base models
3. Updates the results calculation to:
   1. Remove the catch all match by converting the Objective to lowercase and removing the s in the end --> we can not be sure that this is a proper match
   2. Return a NULL and not a 0 when we can not match to clearly message the fact that we do not know how to do that calculation (vs you did not have any results for that date period)
4. Converts the Result Rate from Click to a proper percentage
5. Renames results_per_click to result_rate_from_clicks

Closes #6 (closed)