- use the 'config' field directly

- use the 'field' field directly instead of using the getter just for
  the sake of being able to override it in a unit test. That change does
  require the use of Powermock and Whitebox to be able to set a dummy
  field in unit tests, but makes the actual code more readable.

- use StringUtils.isEmpty to simplify the check in the else-branch,
  and reuse the captionKey variable.

Some outstanding changes (the revert of old Behavior constructs and
their deprecation) still needs to be reintegrated too.

Custom CKEditor extensions may still use this method so it should keep
working in the current minor versions.

CMS-11084 Update drewnoakes-extractor from 2.6.2 to 2.11.0. The library is used to verify an jpg is using YCCK. Note that ImageMetaData has been deprecated some versions ago so should be scheduled for removal.

(cherry picked from commit 8553b57a)

Dropping nekohtml also required replacing its direct usage in HtmlValidator and HtmlDiffModelTest with htmlcleaner.
Also replaced deprecated (Xerces provided) SAXSerializer usage for Console XML Content Export with standard JAXP XMLTransformer.

The code used to setup the RichText link and image pickers should not
be duplicated in the channel-manager.

The DialogManager allows the frontend to provide a custom configuration
in the form of a JSON object. This configuration is merged with the
default configuration that is passed as an IPluginConfig in the
constructor.
To simplify the handling of other parameters coming from the frontend,
I introduced the hook #beforeShowDialog that is called with all request
parameters.

The DialogConfig replaces the ConfigProvider.

Move most of the code into the DialogManager to avoid duplication of
context, config, cancelAction and closeAction.

Also made the distance between several lines of checkbox-label lines match that of the multi-select plugin of Selections.

It is configured with strict.root.path=true so the breadcrumb will not
have clickable labels for ancestor folders of the rootPath.

Use the hippo code style.

Autoboxing is less efficient, and can lead to nasty
NullPointerExceptions when the returned object is null.