Read plugin configuration from kiwi settings

[prawnsalad]

Adding "fileuploader":{ "server": "http://localhost:8088/files" } to the kiwi client config can be read from the plugin via: kiwi.state.setting('fileuploader.server').

Using this format we can get the following configurable while having sensible defaults:

• TUS endpoint (call it server or path for simplicity)
• Max file upload size if uppy supports it