Add cwe_entries as available Issue field

[rachkor]

Summary

This PR adds {{ nessus[report_item.cwe_entries] }} as a new available Issue field

Testing Steps

1. Configure the Mappings Manager like:

{{ nessus[report_item.cwe_entries] }}
{{ nessus[report_item.cve_entries] }}

2. Upload a sample Nessus file and confirm that the CWE (and CVE!) entries appear as expected in the Issues

Copyright assignment

I assign all rights, including copyright, to any future Dradis work by myself to Security Roots.

Check List

• Added a CHANGELOG entry
• Added specs