Clarify the deprecation status of HttpMapperProperties
Add easy way to consume configuration metadata

Add a companion module that IDE developers can use to read configuration
metadata from multiple sources into a single repository.

ConfigurationMetadataRepository provides access to groups and items as
well as an harmonized view on "sources" (that is the POJOs that have
contributed to a given group).

Closes gh-1970
Fix usage of putIfAbsent
Avoid creating a nested group for an Enum

Previously, an Enum that is defined as an inner class of a
@ConfigurationProperties pojo was wrongly detected as an nested group.

This case is now handled explicitly and covered by a test.

Fixes gh-1971
Remove useless @ConfigurationProperties

Fixes gh-1972
Remove useless System.out.println
Associate logging.* properties to group
Revert spring-boot-configuration-metadata for now

See gh-1970
Polish
Refine inner class detection algorithm

Update the ConfigurationMetadataAnnotationProcessor nested class
algorithm to prevent inner classes being added as both groups and
properties.

Fixes gh-1975
Inject ResourceConfig instance (not class) into Jersey

If you inject the class (via a servlet parameter) it seems that
Jersey tries to create all the beans for you (and fails). I thought
it was supposed to work (according to the docs), so I'm a bit confused
but the sample now has Spring DI and the tests pass.

Fixes gh-1981
Use constructor injection for Jersey sample
Lookup metadata bean from context instead of injecting

That way, if there is one, it will always be the right one
(otherwise you might be processing teh parent context with
metadata from the child).

Fixes gh-1982
Update description of property type
Disable Undertow auto-config if required XNIO classes are unavailable 

Fixes gh-1986
Use relative paths so index is unaffected by its context path

Previously, index.html used absolute paths to load its CSS and
JavaScript. This meant that it had to be deployed to /. This commit
updates the HTML to use relative paths for its CSS and JavaScript,
thereby ensuring that they can be loaded irrespective of the context
path to which the application is deployed.

Closes gh-1988
Add an EL implementation to the Undertow Starter

Unlike the Tomcat and Jetty starters, the Undertow starter does not
provide an EL implementation. This leads to failures when you try to use
Hibernate Validator with the Undertow starter.

To bring the Undertow starter into line with the other two embedded
container starters, this commit adds Glassfish’s EL implementation to
the Undertow starter. This is the implementation that’s used by the
Jetty starter. If/when Undertow provides JSP support and, therefore,
starts using EL itself, we should align with it.

Closes gh-1979
Document WebSocket exclusions that are required when using Jetty 8

Closes gh-1969
Add metadata for logging.level

Closes gh-1992
Add metadata for info.*

Closes gh-1993