#SB-213: Switch to maven-indexer:6.0-SNAPSHOT

Committing WIP; tests are broken.
#SB-213: Switch to maven-indexer:6.0-SNAPSHOT

- Added mapping for indexers.
- Fixed indentation.
#SB-213: Switch to maven-indexer:6.0-SNAPSHOT

- Removed unused import.
#SB-213: Switch to maven-indexer:6.0-SNAPSHOT

- Fixed the context issue.
- Minor polishing/refactoring.

#SB-216: Implement a Spring container shutdown listener which closes the indexer and scanner

- Implemented (committing on branch SB-213).
Merge branch 'master' into SB-213

Conflicts:
	strongbox-storage/strongbox-storage-indexing/src/main/java/org/carlspring/strongbox/booters/StorageBooter.java
	strongbox-storage/strongbox-storage-indexing/src/main/java/org/carlspring/strongbox/storage/indexing/RepositoryIndexManager.java
	strongbox-storage/strongbox-storage-indexing/src/test/java/org/carlspring/strongbox/storage/indexing/RepositoryIndexerTest.java
	strongbox-testing/strongbox-testing-storage-resources/strongbox-testing-storage-indexing-resources/src/main/resources/META-INF/spring/strongbox-storage-indexing-context.xml
	strongbox-web-core/src/main/java/org/carlspring/strongbox/rest/SearchRestlet.java
Merge pull request #15 from strongbox/SB-213

SB-213: Switch to maven-indexer:6.0-SNAPSHOT