Add simple analytics

[bzz]

To be able to grow this project UX based on it's actual usage a designer would need to have access to some data.

This issue includes:

• enable Google Analytics conditionally (dev env should not have one, staging deployment should have one, production would have different one)
• as a start, only emit PageView events for every URL change in our FE

[ricardobaeta]

It would be great to know which UI element triggered the URL change.

[dpordomingo]

Yes @ricardobaeta it makes sense and is doable, but I think it should be tracked it in a separated issue, so if @bzz agree, I'd suggest you open a new one.

[bzz]

Analytics was added, subsequent work will be done in separate PRs.