Provide submission attachments to host application

[lognaturel]

User story

As a form designer
I want to be able to specify form fields that capture files
So that they can be accessed from the host application

Todo

• Decide on file naming. Collect uses UNIX timestamps to try to guarantee uniqueness across all media, could still be conflicts in a big deployment. Enketo uses the original filename and appends the hour and minute. Conflicts are very likely. We should decide on a default naming scheme that limits risk of conflicts and ideally conveys some human-readable info. Users would like to name the files.