- add invocation schema customisation
done via fastapi's `Config` class and `schema_extra`. when using `Config`, inherit from `InvocationConfig` to get type hints.
where it makes sense - like for all math invocations - define a `MathInvocationConfig` class and have all invocations inherit from it.
this customisation can provide any arbitrary additional data to the UI. currently it provides tags and field type hints.
this is necessary for `model` type fields, which are actually string fields. without something like this, we can't reliably differentiate `model` fields from normal `string` fields.
can also be used for future field types.
all invocations now have tags, and all `model` fields have ui type hints.
- fix model handling for invocations
added a helper to fall back to the default model if an invalid model name is chosen. model names in graphs now work.
- fix latents progress callback
noticed this wasn't correct while working on everything else.
- add `list_images` endpoint at `GET api/v1/images`
- extend `ImageStorageBase` with `list()` method, implemented it for `DiskImageStorage`
- add `ImageReponse` class to for image responses, which includes urls, metadata
- add `ImageMetadata` class (basically a stub at the moment)
- uploaded images now named `"{uuid}_{timestamp}.png"`
- add `models` modules. besides separating concerns more clearly, this helps to mitigate circular dependencies
- improve thumbnail handling
