In pages specific to a service (e.g. dashboard and sub pages) the title
needs to distinguish which service it applies to. This is mainly to give
context to screen reader users who could be managing multiple services.
Implementing this uses template inheritance:
`page_title` includes `per_page_title` includes `service_page_title`
‘GOV.UK Notify’ is inserted into every page title.
Pages that set `service_page_title` get the service name inserted too.
This PR changes the flow to change an email address.
Once the user enter their password, they are told "Check your email".
An email has been sent to them containing a link to notify which contains an encrypted token.
The encrypted token contains the user id and new email address. Once the link is clicked the user's email address is updated to the new email address.
They are redirected to the /user-profile page.
Also in this commit is an update from flask.ext.login to flask_login.
