Invalidate and refresh customer data sections on HTTP DELETE requests

[Vinai]

The customer-data sections are invalidated and updated whenever a state changing request is sent to Magento.
Currently this happens for POST and PUT requests. However, DELETE is also a state modifying HTTP method, so it would be good if the customer data sections where updated in case of such a request, too.
Otherwise ugly workarounds with POST or PUT to special endpoints like /rest/V1/foo/123/delete have to be created.

Description

This PR updates the client side customer-data model to also invalidate and update the section data for DELETE requests.

I think this is a backward compatible change.

Manual testing scenarios

• Create a REST endpoint that is configured to respond to DELETE requests.
• Create a customer data section that is linked to that REST endpoint URL path.
• Create a JavaScript module that uses the customer-data section and triggers the DELETE request.

Expected outcome:
The customer data section observable updates after the DELETE request.

Actual outcome:
The customer data section is not refreshed.

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[okorshenko]

@Vinai thank you for your contribution!