Add an option to disable SSL verification for Jira

My connections were getting rejected (go figure). This fixed it.
    jira.verify_ssl = False

The default behaviour remains unchanged, so this shouldn't break
anything for anyone whose SSL was already working, or who was connecting
over HTTP.

bugwarrior/services/jira.py

@@ -132,6 +132,7 @@ def __init__(self, *args, **kw):
             options={
                 'server': self.config_get('base_uri'),
                 'rest_api_version': 'latest',
+                'verify': self.config_get_default('verify_ssl', default=None, to_type=asbool),
             },
             basic_auth=(self.username, password)
         )