US #675: Task #1241: Create the button to promote issue to US
US #675: Task #1242: Add references to US in Issue
US #675: Task #1243: Add reference from issue in US detail
US #675: Task #1247: Create the button action to call the api
US #675: Task #1269: Update changelog
Merge pull request #89 from taigaio/us/675/convert-issue-to-us

US #675: Promote Issue to US