[WIP] Replace ECS with Harmony

[mfisher87]

:construction: Work in progress :construction:

• HARMONY_MIGRATION.md will contain my ongoing notes about the migration
• There are some things mixed in here that arguably should be in different PRs. I'm keeping the commits atomic so we can cherry-pick it apart later if we prefer that.
• ...

[github-actions[bot]]

:point_left: Launch a binder notebook on this branch for commit 79169a096371bef5180df2252c978fc0339b0f66

I will automatically update this comment whenever this PR is modified

:point_left: Launch a binder notebook on this branch for commit 01aff4606bbac9fb5647b3c87feeb42b4d6cf8bf

:point_left: Launch a binder notebook on this branch for commit 39b1318af3543c21f90506d76389e76b8243bba1

:point_left: Launch a binder notebook on this branch for commit f65a07c7e160feef730fea05226f3618a372f517

:point_left: Launch a binder notebook on this branch for commit bec4aa3aefb5d3923af9cb0ab083628ae758e979

:point_left: Launch a binder notebook on this branch for commit ac916d6eaa1a1173338962a6ae1fae1de4085826

:point_left: Launch a binder notebook on this branch for commit d67a7be209280724595fa3f679448f4648bb98d0

:point_left: Launch a binder notebook on this branch for commit 402127870ba14532fba6018166678f472139ca62

:point_left: Launch a binder notebook on this branch for commit 4379e1c20e2577aa21328b336ca31adaa5991924

:point_left: Launch a binder notebook on this branch for commit 9638413b3b959be6170c1a9d1f61eca4496c8603

:point_left: Launch a binder notebook on this branch for commit 97e5dc6800da571d427d865d1564a921d30c8880

:point_left: Launch a binder notebook on this branch for commit ba1b00753fd3357731aa6b7c23e267ed40d8cfdb

:point_left: Launch a binder notebook on this branch for commit 014d566562ba504e9a3e0db9e0e996195faff208

:point_left: Launch a binder notebook on this branch for commit f5b4214f04a63e2382f95bb72053d001b1750f05

:point_left: Launch a binder notebook on this branch for commit 0b2f704de1ee173a1c3479f83d7eed80bb64643d