Update ExportCommand.py with file name sanitisation

[gsokoll]

Add "slugify" method to sanitise filenames (removing haracters that aren't alphanumerics, underscores, or hyphens, and strip leading and trailing whitespace, dashes, and underscores).

Addresses issues #19 and #20

[drewnotdrew]

Just tried this, and it solved issues I was having with tapnair's original script. However, I had to add: import unicodedata import re

Am I missing something here, or did you forget to import the unicodedata and re libraries?

[gsokoll]

Sorry, yes I forgot to add those. I originally made changes to the local installation on my PC, and only created the fork and pull request afterwards from memory of what I changed. I will see if I can fix in the pull request.

[ciscoski]

I would also change so that the folder name is sanitized too.

[o-gent]

integrated the closing change and the file name issue here https://github.com/o-gent/Project-Archiver