Add an "issue" task that can display informations about a JIRA issue

For now, only JIRA is supported.

Only one command is available:

      $ albot issues cwt-7
      $ albot issues https://thieriot.atlassian.net/browse/alb-100

Subtasks will be displayed along side the main one.

Note: In server mode, if the JIRA url is detected in a message. Issue will be displayed (Same behaviour as Github PRs)