Interface to allow users to subscribe to push notifications is very buggy

[JimKerslake]

Half the time the button intended to allow users to subscribe to push notifications is not displayed in the UI, despite the user having no row in cspwa_push_subscription table (even dropping all rows from the whole table made no difference).

Other times the button does appear but clicking it has no effect.

Other times an anonymous user visiting the site does prompt creation of a row in cspwa_push_subscription even though they never clicked (or even saw) the consent button.

Other times a user logging in to the site does prompt creation of a row in cspwa_push_subscription mapped against their user id, even though they never clicked (or even saw) the consent button.

And sometimes it does work as intended :)