Dash-leaflet

Changed

- Added ImageOverlay `loaded` property, which is set to `true` when the image has finished loading

Changed

- Leaflet and react-leaflet are now [bundled with dash-leaflet](https://github.com/thedirtyfew/dash-leaflet/pull/146). This structure enables **development of plugins as external packages**.
- Various dependency updates.

Changed

- Changed loading of js chunks so that a chunk is only loaded when actually needed.

Added

- Added [`Minichart component`](https://github.com/thedirtyfew/dash-leaflet/pull/116).

Changed

- The following components are now loaded async: `EditControl`, `GeoTIFFOverlay`, `LocateControl`, `MeasureControl`, `MarkerClusterGroup`. As a result, the main bundle size has been reduced to about half (< 500 kB).
- Update to Dash 2.0.
- Prop validation of `GeoJSON` component `hideout` prop relaxed.
- Prop validation of `Polygon` component `positions` prop relaxed.

Added

- Added `drawToolbar` and `editToolbar` props to `EditControl` component.

Changed

- Polygons collected into the `geojson` prop of the `EditControl` component are now closed.

Added

- Added `EditControl` component.
- Added `GestureHandling` component.
- Fixing [issue](https://github.com/thedirtyfew/dash-leaflet/issues/95)
- Fixing [issue](https://github.com/thedirtyfew/dash-leaflet/issues/96)