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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When this was written years ago we only supported JExcel (because we only needed support for xls files). When open sourcing it support for poi (and the abstractions) where added. I would favor deprecating it jus like in Spring itself. 

Another question this is removed, what sense does the abstraction have we could drop that all together.