Provide feature suggestion when config element is for feature that is not configured

[cherylking]

Provide feature suggestions when config element is used but the feature is not currently configured. WDT does this by generating a featureList.xml file which maps config elements to their features.

This is a future enhancement and not part of the MVP. Slide 36 of UFO.

[cherylking]

Implementation notes:

1. Generate feature list for installed runtime. Process the feature list to gather data.
2. Create a map where the key is the config element and the entry is a collection of feature names that utilize that config element.
3. Validate that each config element in a Liberty configuration file is supported by a feature in the featureManager list.
4. Issue a diagnostic for any config element without a related configured feature, and a quick fix with a list of possible features to add that support that element.

Question: Do we need to consider included files and the features they add, as well as the configDropins files (defaults and overrides)? Can first pass of support just consider the features within the same file?

Second question: What about features that automatically pull in other features? Are all the config elements accumulated in the feature list?

[cherylking]

Side note: Could also collect the list of features enabled by each feature when processing the feature list. This is needed to support issue #164.

[cherylking]

Now that this is merged, the only piece not handled is the big picture of all features that are configured across all Liberty configuration files (server.xml can include other xml files, and configDropins can contain config snippets). I will open a separate issue for this.