Enable retrieving component-specific issues

Many projects are divided into smaller components (managed in Maven via multiproject). Usually, the same structure is reflected in the project's JIRA - meaning a big project with each smaller project mapped to a JIRA component.

If we add the JIRA report for such projects (that are part of a larger project), all subprojects will show all JIRA issues for the project, instead of the issues relevant to that specific component.

Therefor, it would be useful to specify for the JIRA plugin to only query issues for a specific component, based on a plugin property. Then, each subproject will specify that property in its project.properties file, thus reflecting the true JIRA structure in the JIRA report.

Attached to this issue is a patch I've made that makes it possible.