When attempting to upload a large file, MyTardis should give an error, not fail silently

[wettenhj]

There are known issues with MyTardis using too much memory (on the server) when we allow large file uploads (> 1 GB), so we usually restrict the maximum file upload size in our nginx config, and since Django 1.10, there's also the DATA_UPLOAD_MAX_MEMORY_SIZE setting which we override in our tardis/default_settings/uploads.py. If a user attempts to upload one or more files which exceed this limit, MyTardis should display a user-friendly error, instead of failing silently.