[WIP] Minor improvemnts in sonata_type_model_autocomplete

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | yes, but minor (removed some default CSS classes)
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets |  -
| License       | MIT

refs #1764

- [x] fixed initial width of input field (with `form-control` class)
- [x] added `width`, `container_css_class`, `dropdown_item_css_class` options
- [x] removed unneeded default CSS classes `sonata-autocomplete-dropdown` and `sonata-autocomplete-dropdown-item`
- [] testing for all use cases