[maven-release-plugin] copy for tag dnet-download-plugins-2.1.6
added D-lib plugin
added regular expression parameter for download plugin
added log
added plugin for HAL
npe check
added further logs
changed plugin of download of Arxiv in accord to the ticket #903
Changed plugin signature
re-formatted code
Added plugin of download for portuguese repos
Added check on open access before download
Added plugin for E-LIS
added files