Kind composer

I'd like to support the following workflow:
1. Paste a hex-encoded data.
2. Add "kinds" that compose a particular type (type + name (optional - autofilled)).
3. At the very end always display remaining bytes as some special field.

Could be done by selecting "Compose" at the regular selector, which would open up additional section between input and controls that would allow composing the type.
The type should also be possible to describe as JSON-like format, like so:
```
{
"id": "u8",
"name": "string",
"header": "Header",
"blob": "blob"
}
```
So that the composed type can be:
1. locally persisted
2. added to the URL
3. Copy & Pasted over chat