Email Import returns Invalid file upload. -- due to issues parsing URLs that are base64 or quopri encoded

In trying to upload an EML for parsing which had a base64 encoded body, MISP returned "Invalid file upload." The cause is that we had URL parsing enabled and it only looks for HTML parts to parse not base64 or quopri. Please see about adjusting the code to look for these conditions as well.

Example:

Current code: if (extract_urls is True and part.get_content_type() == 'text/html'):

Future code:

for part in message.walk():
	decoded_part = part.get_payload()
	if part.__getitem__("Content-Transfer-Encoding") == "quoted-printable":
		decoded_part = quote_printable_decode(part)	
	elif part.__getitem__("Content-Transfer-Encoding") == "base64":
		decoded_part = base64_decode(part.get_payload())	
	if part.get_content_subtype() == "plain":
		all_urls.extend(get_urls_from_plain(decoded_part))	
	elif part.get_content_subtype() == "html":
		all_urls.extend(get_urls_from_html(decoded_part))

Start by locating the email-import code containing extract_urls, message.walk(), and the text/html condition. Reproduce the supplied EML case and trace how each part's content-transfer encoding is handled. Done means URL extraction works for base64 and quoted-printable plain or HTML parts without returning "Invalid file upload."