Add customer's email address to "Order Line Items" report-format output

[lat9]

... as requested in this Zen Cart support-thread posting.

[jage9]

I have made this mod on my store and can submit as a PR if desired.

• Adds Email address column to table display and CSV for the order level reporting
• Email is pulled from the order itself, so is the Email address as of the time of the order, consistent with name handling
• Added appropriate language file entry for heading

If this messes with the visuals, could explore just making this available for the CSV, or an optional field, though there is not currently a way to hide plenty of other fields.

I looked at adding Email into the list of sort fields, but that feature seems to not be working as expected in 3.4.0 unless I'm misunderstanding it.

The major use case for me is to easily gather a list of Email addresses for an ordered product, to provide an update, recall, or other info. Perhaps it makes more sense to use the current customer Email address if available, but again the first/last from the order record is what's currently being used, so tried to remain consistent. One could argue this is a bit outside of the purview of a sales reporting mod, but it allows for easy customer follow-up based on sales, so I think it fits, at least until there is another solution. Certainly open to feedback.