Don't show addon categories that have less than N extensions available.

[KevinMind]

Describe the problem and steps to reproduce it:

There are X places in AMO where categories and their related extensions are displayed. If a category doesn't have any extensions or has below some acceptable threshold number of extension then we should not display those categories on AMO.

What happened?

Empty categories can be seen on AMO

What did you expect to happen?

They should be hidden from the Frontend on discovery areas.

Anything else we should know?

We shouldn't "disable" these categories, you should still be able to interact with them, we should just filter them from the specific UX areas where having a minimum number of extensions is relevant.

We should find all of the areas where this problem is relevant

We should decide how many extensions is the minimum number.

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