Releases for Feeds XLS

Fixes #2449265: Empty Nodes in Large Import

• Compare headers without requiring the text case to match. #2194903: lowercase header values to be consistent with FeedsCSVParser
• Tweaked the code based on the patches in #1461832: Cannot map to a date field so we're now using PHPExcel_Shared_Date::ExcelToPHPObject() to convert the date/time rather than mktime(). Note, the current methodolgy allows for dates to be entered as strings aswell as numeric values.
• Simplify the loading of the library, and also ensure users can simply download the library, extract and rename without having to move the classes folder. #2021965: Standardise PHPExcel library install path to match PHPExcel github repo
• Ensure empty values are not imported into list fields
• Allow importing of "0" into numeric and string fields
• Other fixes from upstream repository (https://git.scratchpads.eu/v/scratchpads-2.0.git)