[Advanced Timeline] Disable alltogether until it works
@bilboed
Submitted by Edward Hervey Assigned to Edward Hervey @bilboed
Description
The advanced timeline is confusing a lot of users.
Since work isn't concentrated on it currently, it should by default be disabled and not visible in the UI.
We should have a environment variable to allow users who wish to to have it enabled though.
Imported from https://bugzilla.gnome.org/show_bug.cgi?id=432644