Update page title and links relating to Manage Subscriptions page

Pretty well covered by behat, but here's a quick test to confirm all looks as expected: Log in as any user and navigate to the dashboard. Add the calendar block if it is not already visible. CONFIRM below the calendar in the calendar block, you see "Full calendar" and "Import or export calendars" links. Click the "Import or export calendars" link. CONFIRM you are taken to a page with URL in the format "<yoursite>/calendar/managesubscriptions.php". Navigate to a course page, then click on its calendar link in the side navigation. CONFIRM you are again taken to a page with URL in the format "<yoursite>/calendar/managesubscriptions.php". CONFIRM in the title of the page, you see "Import or export calendars" and not "Manage subscriptions". CONFIRM below that heading, you see an "Imported calendars" heading (and not "Your subscriptions"). Right click the "Imported calendars" heading and select "Inspect". CONFIRM the heading has an "aria-describedby" attribute, which has the value "subscription_details_table". Click on the "Import calendar" button. CONFIRM in the page breadcrumbs, you see "Import or export calendars". In the page breadcrumbs, click on the "Calendar" link. CONFIRM that below the calendar there is a single link, "Import or export calendars". CONFIRM that clicking the link returns you to the page you were on in steps 5-9.