Make manual uploads more resilient

[Amdrel]

Looking at the upload code that we currently have we don't specify any retry options and the upload function gives up the moment anything goes wrong. Users uploading large files may have unstable internet connections or the connection to the server may get briefly interrupted for other reasons. We need to handle this better.

[Amdrel]

There's documentation on how to do this here: https://github.com/blueimp/jQuery-File-Upload/wiki/Chunked-file-uploads

It's also worth noting that the library we're using to upload files hasn't been updated in almost 3 years. It might be worth replacing it. This dependency in-particular is what held me back from upgrading jQuery to the latest major version. We can probably use something else.