Prevents warnings in the console about unhandled rejections. We can
safely catch and ignore these errors, because they also show up in the
UI already anyway.
This PR adds support for extracting metadata from `<form>` elements.
This was asked #153 and came up elsewhere too, I believe. You can use
it like this:
```html
<form class="MyForm" action="/">
<input type="file" />
<input type="hidden" name="bla" value="12333">
<input type="text" name="yo" value="1">
<button type="submit">Upload</button>
</form>
```
```js
uppy.use(DragDrop, {
target: '.MyForm',
locale: {
strings: {chooseFile: 'Выберите файл'}
},
setMetaFromTargetForm: true
})
```
Then UI acquire type plugins, like Dashboard, FileInput and DragDrop,
before mounting themselves or doing anything else, extract FormData
from the `target` `<form>` element (it must be a form currently), and
merge the object with the global `state.meta`. This is done via
`setMeta` method on core. Then, when a file is added, `state.meta` is
merged to that file’s meta right away. The ability to add more fields
via UI plugin MetaData is also still there, though probably needs an
update.
In addition a new `meta` option is added in core:
```js
const uppy = Uppy({
debug: true,
autoProceed: true,
meta: {
username: 'Artur'
}
})
```
This way some data can be set right away, it becomes the initial
`state.meta` object.
Allow a configurable input name in the FileInput plugin with a default of `files[]`. This functionality matches the Multipart plugin.
Add basic unit tests for `inputName` FileInput constructor option.
