[MSHARED-1407] Track dependency usage by referencing classes

[jaredstehler]

This enhances the functionality which shows specific classes in use per dependency, by mapping those uses to classes which are referencing them.

The resulting API addition is:

Set<DependencyUsage> analyzeUsages(URL url, ClassesPatterns excludeClasses)

which I plan on adding a PR to maven-dependency-plugin to show how we use this feature in practice.

This was originally proposed via this PR #20 which was closed due to lack of support for default interface methods prior to JDK8.

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[jaredstehler]

Updated with all inadvertant formatting and import changes reverted.