Fixes #2581.

- jQuery to version v3.3.1
- Bootstrap-datetimepicker to v2.4.4
- jQuery mousewheel to v3.1.13
- Inputmask to v3.2.7
- jquery-sortable to v 0.9.13
- Remove jQuery UI from our static files. It has not been used for a long time in core.

Inputmask has a newer version but it doesn't work in the way that we use it. We will need to upgrade that separately later.

Use npm and gulp to manage the static files for all these dependencies.

Also remove deprecated `charset` and redundant `type` attributes from all script tags.

Also use npm to manage the dependency, and gulp to copy the files into our static directories.

Usage:
  npm install
  npm run build
  npm run start