Changes files components (`FileUpload`, `FilePicker`) so that
their API returns the whole `fileJSON` instead of just and `id` (and
`kind`)
This is needed, for example, in image emebeddable to also get an
blurHash after uploading or picking an image without fetching the whole
file again.
* implement copy updates
* move rename file and update empty state copy
* update title to respect multi select vs single select
* added test for single select behaviour
* implement single select behaviour
* introduce and use multiple prop, default true
* pass multiple flag to state
* pass multiple upload flag to UI
* added single select story
* update files example to still support multiple select
* uploadMultiple -> selectMultiple
* remove use of non-existent i18n
* update filepicker react component tests
