On staging and production servers share the cookie between subdomains

[buren]

We want to detect whether the user is logged in on other subdomains than app.justarrived.se.

This PR updates the cookie storage code to share its cookie with subdomains of justarrived.se and justarrived.xyz

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@bex1 will this cause any problems with server side rendering?

[buren]

The CI is failing because it installs yarn v1.1 which is incompatible with our version of node (v6.11). We should probably upgrade our node version its quite out of date.

We're not going to be able to deploy if heroku decides to use yarn v1.1..

[bex1]

👍 Nice! LGTM