Track apiv2. Fixes #823

Tracks API v2 calls as GAnalytics events. The Event Category is "api-v02" (as opposed to "api" for v01). By selecting 
Secondary dimension > Custom Dimensions > X-TBA-App-Id, we can see which apps are making which calls.

For the custom dimension to show up, go to the correct Account and Property in GAnalytics's Admin page > Custom Definitions > Custom Dimensions > New Custom Dimension. Name: X-TBA-App-Id, Scope: Hit, Active: Checked.