Bug in email signature detection

Issue Summary

As per https://jira.atlassian.com/browse/JSDCLOUD-5878 , the signature functionality has been rolled out, but none of it is filtered out, even despite the custom rules being as set.

Steps to Reproduce

1. Enable HTML parsing
2. In Hide email signatures in issues and portals check both the boxes, Use Default detection to hide signatures and use custom text to detect and hide signatures.
   Add custom text like Kind regards etc..

Expected Results

We should be filtering the signatures which has the custom text.

Actual Results

Sometimes when the customer uses a custom text, there are some special characters in the HTML text similar to the one given below, and because of which the regex matching is not working. These characters should be removed from HTML before doing the regex match. 

Met vriendelijke groet, With kind regards, Mit freundlichen Grüßen 

Workaround

Currently there is no known workaround for this behavior. A workaround will be added here when available