add a whole bunch of category fixes

[AstridKery]

This MR pulls together a whole bunch of little updates, mostly related to the recent category update:

• moves the label serializer code to only run in get_labels if labels < 100
• makes the category case-insensitive, so that the metadata fields with different capitalization in their name can be matched
• adds loading spinners to the label upload page and the project creation page to avoid confusion
• BUG FIX: closes a loophole in the annotate_data function so that if someone just labeled the item in the history table it won't make a second label
• slightly modifies the codebook rendering to not run a bunch of the slower code when there is no codebook
• adds an "all" category to the label category dropdown so that someone can search all labels if needed
• fixes the null description/metadata rendering so that they just aren't shown instead of having "nan" everywhere

[AstridKery]

This looks good to me. The only thing I did that kind of broke it was

1. Create a project with matching data and label metadata (category column = State)
2. Go to the update label descriptions page
3. Re-upload the label file but the category column name is changed to sTatE Results in screenshot below. But I feel like it might be safe to assume that no one would do this?

Thanks! I had been toying with adding case-insensitive checks to the file reads. This confirms that it would be a good idea. I didn't even think of someone just changing a field name, but that's possible. I've added that in now.