Purchases: Add analytics for sections in /purchases

[scruffian]

Fixes #271 (well part of it)

This adds analytics calls to the single-purchase pages in /purchases.

Testing

1. git checkout fix/12207-analytics
2. Open http://calypso.dev:3000/purchases
3. Add calypso:analytics to the debugger so you see analytics calls in your console
4. Assert that you see these events:

• calypso_cancel_private_registration_purchase_view
• calypso_confirm_cancel_purchase_view
• calypso_cancel_purchase_view
• edit_card_details_purchase_view
• calypso_manage_purchase_view

calypso_edit_payment_method_purchase_view is also included in EditPaymentMethod in this PR, but that component doesn't appear to be linked from anywhere right now.

The events should have a product_slug property.

• Code review
• QA review

[fabianapsimoes]

I'm having issues loading /purchases in this branch:

Error: Invariant Violation: ReactClassInterface: You are attempting to define goToManagePurchase on your component more than once. This conflict may be due to a mixin.

[scruffian]

I'm having issues loading /purchases in this branch:

Sorry, my mistake. It should be working now.

[drewblaisdell]

Are we ever going to override the default trackingSlug by using the prop? If not, we should probably just store it as a property of the class and access it with this.trackingSlug in purchasesMixin.

[scruffian]

Good idea

[gziolo]

Once we have #586 it needs to be rebases. Maybe we should also create utility method for analytics?

[drewblaisdell]

I rebased, moved the recordPageView function to utils, and added it to each of the sections.

[scruffian]

LGTM 👍

(Feels weird doing that on my own PR, but none of the commits are mine)