customize indexing with exclusion patterns

[san-zrl]

PR for issue #29

• Replaced exclusion predicate with customizable patterns
• Matching is performed on relative paths w.r.t project directory
• Exclude file/dir from indexing if any pattern matches
• <indexer>.setExclusionPatterns(List<String> patterns) sets patterns
  • Patterns are java regexes that match on the first occurrence
  • Default patterns
    • Python src/test/, tests/
    • Java src/test/, /package-info.java$, /module-info.java$
  • Passing null -> re-establish default
  • Passing empty list means no exclusion -> index everything