Dash-devices

Added
- [967](https://github.com/plotly/dash/pull/967) Add support for defining
clientside JavaScript callbacks via inline strings.
- [1020](https://github.com/plotly/dash/pull/1020) Allow `visit_and_snapshot` API in `dash.testing.browser` to stay on the page so you can run other checks.

Changed
- [1026](https://github.com/plotly/dash/pull/1026) Better error message when you forget to wrap multiple `children` in an array, and they get passed to other props.

Fixed
- [1018](https://github.com/plotly/dash/pull/1006) Fix the `dash.testing` **stop** API with process application runner in Python2. Use `kill()` instead of `communicate()` to avoid hanging.
- [1027](https://github.com/plotly/dash/pull/1027) Fix bug with renderer callback lock never resolving with non-rendered async component using the asyncDecorator

Fixed
- [1006](https://github.com/plotly/dash/pull/1006) Fix IE11 / ES5 compatibility and validation issues
- [1006](https://github.com/plotly/dash/pull/1006) Fix bug with renderer wrapper component TreeContainer to prevent useless re-renders
- [1001](https://github.com/plotly/dash/pull/1001)
- Fix and improve the `clear_input()` API in `dash.testing`, so it's more robust handling react `input`.
- make the `percy_snapshot()` API more robust, and the timeout of `wait_for_callbacks` (if set to True) will not fail the snapshot execution, but logged as potential error.

Fixed
- [999](https://github.com/plotly/dash/pull/999) Fix fingerprint for component suites with `metadata` in version.
- [983](https://github.com/plotly/dash/pull/983) Fix the assets loading issues when dashR application runner is handling with an app defined by string chunk.

Fixed
- [987](https://github.com/plotly/dash/pull/987) Fix cache string handling for component suites with nested folders in their packages.
- [986](https://github.com/plotly/dash/pull/986) Fix a bug with evaluation of `_force_eager_loading` when application is loaded with gunicorn

Added
- [964](https://github.com/plotly/dash/pull/964) Adds support for preventing updates in clientside functions.
- Reject all updates with `throw window.dash_clientside.PreventUpdate;`
- Reject a single output by returning `window.dash_clientside.no_update`
- [899](https://github.com/plotly/dash/pull/899) Add support for async dependencies and components
- [973](https://github.com/plotly/dash/pull/973) Adds support for resource caching and adds a fallback caching mechanism through etag

Fixed
- [974](https://github.com/plotly/dash/pull/974) Fix and improve a percy snapshot behavior issue we found in dash-docs testing. It adds a flag `wait_for_callbacks` to ensure that, in the context of a dash app testing, the percy snapshot action will happen only after all callbacks get fired.

Fixed
- [969](https://github.com/plotly/dash/pull/969) Fix warnings emitted by react devtools coming from our own devtools components.