Show processing message when upload done but not processed

[Hattorius]

Currently when uploading large files the progress bar slowly moves to 100% based on how far it is with the upload process. When it reaches 100% the full file has been uploaded but still needs to be processed on the server side (additional encryption etc.). This can take a while for large files.

Proposed solution
After the file upload progress reaches 100% here:

CipherDrop/frontend/index.js

Lines 59 to 64 in 6957b64

	xhr.upload.onprogress = event => {
	if (event.lengthComputable) {
	let percentComplete = (event.loaded / event.total) * 100;
	this.progress(percentComplete);
	}
	};

it should show the message "processing"