S3FileStore & more

This branch adds:
- FileStore support
- configurable AmazonS3Factory support (for injecting custom S3 client's)
- fully customizable AmazonS3Client configuration options (via environment variables, System properties, amazon.properties file or a directly provided java.util.Map<String, ?>)
- AmazonS3Client RequestMetricCollector support
- Multiple S3FileSystem support

with 100% UnitTest Line Coverage (and 95% Branch Coverage according to cobertura).