Add some tweaks to the project creation code

[AstridKery]

• remove full file limit (allow users to upload files with no unlabeled data)
• when someone uploads a file with labels not defined in step 2, just print the extra labels instead of both full label sets (this works much better when there are many labels)

[AstridKery]

Things to look for in this merge request

• when someone is looking to upload data to the project, SMART should no longer throw an error if the file only has labeled data. Reviewers should make sure that uploading a full file when creating the project doesn't lead to any unexpected behavior downstream in the project (i.e. when someone goes to the annotate page, when someone uploads unlabeled data), especially in the cases where the modeling or active learning features are turned on.
• try uploading a label file with a new label not defined in step 2 and see if the error printed to the user makes sense
• look at the label upload directions and see if they make sense

[andykawabata]

This looks good as far as I can tell.

• I uploaded a fully labelled dataset and could not break anything while clicking through annotation pages
• The error message when uploading data with bad labels was clear. Worked both on the initial data upload and when updating data.
• The label upload instruction seemed mostly clear. I did leave one comment with a suggestion.