improvements and bugfixes for downloading files

depends on clientlib-java v1.1.0; see daisy/pipeline-clientlib-java#1

 * fixed issue where the selected tab in admin settings were seemingly random each time you updated the page
 * no more references to port 8182, 8181 is the only default from now on
 * the webui is now required to run on the same filesystem as the engine. Results are downloaded directly from disk. fixes daisy/pipeline-issues#375
 * the correct content type is now returned when downloading single files
 * "an e-mail will be sent to user ..." in create user form now only shows when email is enabled
 * filenames are improved for downloads. fixes daisy/pipeline-issues#385
 * this seems to fix daisy/pipeline-issues#381 as well, although the issue haven't been adressed specifically