dependency tracker should be project-specific, not global

[martinlippert]

The SpringIndexerJavaDependencyTracker that is used on SpringIndexerJava is a global object in the indexer that is used and stored across all projects in the workspace, even though it contains information that is usually very project specific. Therefore, the dependency tracking should be made project specific.

[martinlippert]

This work should probably also include a cleanup mechanism as well.