BATCH-2041: Add support for reading excel files

This commit adds support for reading Excel files. Both JExcel and Apache POI are supported. Support for reading Excel files has been designed similar to the support for reading flat files.

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This isn't correct.  Per `Resource`'s documentation, a `Resource` should return "a fresh stream" which means that this is just opening a stream and closing it again, instead of closing the stream that was being read during regular processing.  See: http://docs.spring.io/spring-framework/docs/4.1.x/javadoc-api/org/springframework/core/io/InputStreamSource.html#getInputStream--