There are several things to focus on in this ticket:

[x] Use the workspace feature to set up the various workspaces.
[x] Separate the common utility functions into a separate library (some will go with the models, some will go with Yaati).
[x] Move the Yaati library into a separate workspace from the UI.
[x] Move the models into their own workspace.
[x] Break apart the various data brokers (Localstorage, ProjectProfile, and the future hREA one) into a data providers directory either in the Yaati library or in its own workspace.
[x] Refactor the path methods out of the models into another common structure.
[x] Refactor the data-providers to use the new structures.
[x] Abstract away our Root data structure from the Yaati Library so we (and others) can use it in more contexts.
[x] Write some tests for some of the basic functions everything is built from.
[x] Our main Application DataStore.ts is still tightly coupled to the models having paths.
[x] Make sure all the rest of the code uses the new Pathed data type and imports are updated.
[x] Break apart the major features provided by Yaati into about four mixins.
[x] Write additional tests for the Yaati core.
~~Optionally, make a path generator that uses the TreeDefinition to make the correct template strings for paths.~~

Notes about what's left to refactor

ui/src/elements.ts

I don't think we can do much with this now. But it will almost completely disappear with https://github.com/lightningrodlabs/rea-playspace/issues/118#issuecomment-1254753106

deferOnChange<T> (name: string, value: T, onChange: ({}) => void)
slChangeConstructor<T> (name: string, onChange: ({}) => void, setState: ({}) => void, parsers?: {}, validator?: ({}) => boolean)
padBy2 (n: number): string
getDateParts (dt: Date)
DateToInputValueString (dt: Date): string
DateToUiString (dt: Date): string
NumberToString (value: number | string): string

[x] Move to typed-object-tweezers.
rejectEmptyFields<T>(unfiltered: T): T — not used?
assignFields<T extends Object, U extends Object>(unfiltered: T, context: U) — used everywhere, but definitely needs to be a part of Yaati
overwriteFields<T extends Object, U extends Object>(unfiltered: T, context: U) — not used
toJSON<T extends Object, U extends Object> (context: U): T — used in all models
fieldsToJSON<T extends Object, U extends Object> (context: U, fields: Array<string>): T — used in a few models
objectsDiff<T extends Object> (A: T, B: T): boolean — used in FlowModal
traversePath (tree: {}, path: string, hasObject: (cursor: {}, slug: string) => void, noObject: (cursor: {}, slug: string) => void, skipRoot: boolean = false, checkRoot: boolean = false) — used in localstore
getPath (tree: {}, startPath: string, skipRoot: boolean = false, checkRoot: boolean = false) — used in localstore, YatiReactHook, YatiTreeStore
traverseTree(tree: {}, startPath: string, pre: (path: string, obj: {}) => void, post: (path: string, obj: {}) => void, oldPath: string = '') — used in localstore and YatiTreeStore

Part of Yaati.

Part of Yaati.

The general hooks for data stores.

The wrapper for a Svelte Readable.

Let's keep this where it is for now.