Spreadsheet And CSV Export

New feature that's probably one of the oldest outstanding requests, exporting the content of the main window to a file!

There are two ways to export, both accessible by right clicking the list, "export selected" and "export all". What they do is hopefully self-explanatory. You will also have two options for file types for the export, Office Open XML (.xlsx), and semicolon delimited text (.csv).

Why xlsx and not some other format like ods? Mostly on account of PicoXLSX being the smallest spreadsheet writing library I could find.

As ever, if there are any issues let me know.