NX-392: Completely remove old plugin manager and related classes
NX-392: improve startup performance (GLOBAL_INDEX maps to getResources which is faster than findEntries for bundles with embedded jars; when we move to fine-grained bundles we can go back to INDEX)
NX-392: cleanup logging
NX-392: use ApplicationDirectories to access ${nexus-app} path
Add nexus-app property to legacy IT client
Merge pull request #498 from sonatype/NX-392-remove-plugin-manager

NX-392: Completely remove old plugin manager and related classes