Don't restrict regions for paid (bug 904157)

This is a branch to remove the restrictions for addon exclusion records for paid apps.

**Don't merge yet - this has deps**

See bug https://bugzilla.mozilla.org/show_bug.cgi?id=904157

This requires a bunch of changes ahead of this branch to be possible namely these bugs:

https://bugzilla.mozilla.org/show_bug.cgi?id=913105  Re-index paid apps when a Price Currency changes (RESOLVED FIXED)
https://bugzilla.mozilla.org/show_bug.cgi?id=913123  Update featured apps code to take into account pricing data
https://bugzilla.mozilla.org/show_bug.cgi?id=909532  Change lookup for a regions on a paid app for search

These will all be done ahead of this branch landing in other branches.

This branch makes the regions the user can be excluded from independent to the price region data so we're not trying to amend the exclusion records based on what price the user has selected. Doing this makes it easier to enable the users' app in the new regions when they have payments enabled (assuming relevant to the price).

This change also makes use of a new field for whether the app should be automatically enabled for new regions. This is instead of using worldwide to track this so we have the same field for both free and paid apps. In both cases worldwide is just treated as a.n.other region.