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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Just realized that I have a couple of people using my initial version of the excel stuff and I know that some of them are on jExcel. So making it deprecated in the initial release and removing it later on would give them a migration path. 

Just a thought...