[DS-1688] Add UI support for BTE batch metadata import

Administrative UI support for BTE batch metadata import.

The user can select the data file to upload, the type of the datafile (bibtex, csv, etc.) and the collection that the items should be imported to and then the BTE runs to import the data.

Mapfile generated by the import is saved and the user is informed via email regarding the status of the import (like the export stuff...)

The corresponding service is accessible via the administrative sidebar.


This pull request is build based on the PR: https://github.com/DSpace/DSpace/pull/317 

Related Jira issue: https://jira.duraspace.org/browse/DS-1688