Implement a basic importer of Jira's issue.

The old implementation, based upon HTML-scrapping, was completely
removed. Instead, we opted out for a new implementation using
JIRA's REST services.

Our first try was using the "official" JIRA's REST client. However,
that didn't worked out properly: errors 404 was thrown upon us,
even though the configuration was properly set up. Thus, we
implemented our own REST client using Jackson JSON and IroniaCorp-Commons-Http
(which is a wrapper for Apache HttpClient 4).

Currently we can successfully import a single issue (without comments).
Parse several issues and comments at once.
Parse a single full issue from a JSON file generated from JIRA.
Update issue's priorities and status with values used by Apache Hadoop.

Read that from REST service. We try to read 50 each time, sleeping by
2 minutes between reads.