Allow for data import between different versions of Jira

Now PC can be enabled to import complete projects from an instance running a different version of Jira than the target. This will save time and provide a lot of extra flexibility to users.

This feature can be enabled by checking the "Allow data import from different Jira versions" radio button at the "Import complete project" page, as shown in this image:

Please note, that importing data from different Jira versions might eventually lead to not all information being imported or other import problems. This risk would be greater as the difference between the source and target version becomes larger. If this option is enabled, the plugin will display a warning about this risk.