A 4-category from Khovanov homology

We'll work towards describing a 4-category built using Khovanov homology.

We'll start with a reminder of what Khovanov homology does (at least as a black box). There are then two different routes towards describing the "4-dimensional nature" of Khovanov homology --- we can explain how to build a "braided monoidal 2-category" using Khovanov homology, or we can explain how to build a "lasagna algebra", and from that a "disklike 4-category".