Finish basic PoC: Creating JIRA issue creates new SFCase w/subj & desc
- Delete old JIRANewIssueHandler class, replace with new class that
    reflects that it is an API resource APIResource_JIRA_Issue
- Change Endpoint to /jira/issue/*, indicating issue as resource
    -> So for example, POST to /jira/issue, GET to /jira/issue/{id}
- Implemented createIssue method, takes subj and desc and creates Case
- Update README to reflect endpoint/resource change
- JIRAIssue class updated to include webhook nature