feature(Datepicker) docked plugin implementation

[gselderslaghs]

Proposed changes

This pull request is a follow up of #582 and implements the docked display plugin

Usage:

displayPlugin: 'docked', displayPluginOptions: { // specify options here } 

Types of changes

• Bug fix (non-breaking change which fixes an issue).
• New feature (non-breaking change which adds functionality).
• Breaking change (fix or feature that would cause existing functionality to change).

Checklist:

• I have read the CONTRIBUTING document.
• My commit messages follows the conventional commit format
• My change requires a change to the documentation, and updated it accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[wuda-io]

The onConfirmed and onCancel should be removed from the Datepicker in a next refactor.

[wuda-io]

👍