Add analytics w/ page views via Countly

[terichadbourne]

This PR adds tracking via Countly (hosted at countly.ipfs.io) while respecting "do not track" requests in the user agent.

It taps into Vue's routing system to allow us to see the path for any resource that has its own path, such as tutorial landing pages and individual lessons:

This PR also removes tracking via Google Analytics. (Will this cause any problems for you, @mikeal?)

This PR does not address event tracking, such as clicks on "reset code," "view solution," or "submit" buttons within lessons. We'll plan to address that in a second PR once this is in place.

Note: If testing on localhost, you'll need to comment out line 70 in index.html (which restricts tracking to views of the live website) and uncomment line 65 (which tracks views on localhost as well).

Pair programmed by @olizilla & @terichadbourne

[terichadbourne]

Closes #179

[terichadbourne]

@olizilla You mentioned something about potential cross-site issues with Safari. Should I run on localhost in Safari as the test for this and see if Countly catches my views?

Was there something we need to do to check for when there's no Countly to reference? (Or maybe that's already dealt with by the order of the code?)

[fsdiogo]

LGTM 👍

[terichadbourne]

@olizilla I tried testing from Safari and no page views are registered. If I understood you correctly, this is because we're hosting the Countly instance on ipfs.io instead of proto.school, right? How much work would it be to create a separate instance on the other domain? I went to our existing Google Analytics and see that 16% of our visits over the past month (18% since launch) have come from Safari, so it's a reasonably sized chunk of data we'd be missing, including anyone who receives a link to ProtoSchool on Twitter or otherwise on an iPhone and clicks directly rather than making an effort to open their favorite browser. Should we plan on moving the Countly hosting? Perhaps we adjust this PR to keep GA enabled until that change is made?

[terichadbourne]

@olizilla helped me figure out why my Safari visits weren't being tracked, and the setup is actually okay as is. After we merge we'll need to test again from Firefox to confirm the cross-site tracking is working (since there's an exception for localhost). If it's not, we'll need to host Countly on proto.school instead of ipfs.io.