Front end:
the new tracker creation a new section "create from jira"
enable user to :
- enter is connection information (server url, username, token)
- then choose a project and a tracker

Backend:
The import covers jira fields that can be easily mapped to Tuleap fields:
* string
* text
* lists with static values

With this patch:
- tracker structure for fields is created
- tracker structure must also include tuleap specific field artifact_id and an external link to the jira original artifact
- artifact is imported
- semantics title, description ans status are imported
- the default report is created
- import is done asynchronously