Large downloads for non-authenticated users

**Is your feature request related to a problem? Please describe.**
We can easily provide the option of direct downloads for non-authenticated users. This means, however, that the current functionality of Peace Portal - downloads up to 10'000 documents - would not be provided anymore.

**Describe the solution you'd like**
As described before in #1229, we could let non-authenticated users enter an email address in the download dialog, to which the download link will be sent after completion. This address should not be saved to the database, however (privacy by design).

**Describe alternatives you've considered**
As we can somewhat reproduce the current behaviour of the Peace Portal servers by just setting the maximum size for direct download to 10'000, this issue perhaps doesn't have highest priority or might be even a "won't fix" - for the regular I-Analyzer servers, users can make a user account in order to get larger downloads.

**Additional context**
Perhaps the maximum download size for direct download could also be higher? I think that downloads of up to 10'000 documents can usually be done in a short enough time that the email functionality might not even be necessary. We could even add two settings to a corpus - the max size for direct downloads and the max size for any download (this cap may be removed for users through the permission system). A setting for the direct download cap would be a good idea anyway: right now, both backend and frontend have this number hard-coded.