Add progress bar, summary page, resume where you left off, consolidate backend

[bzhang625]

Summary:
Added progress bars for batches and words, a summary page to view current labels and unlabeled videos, resume where you left off button in batch selection page, and consolidated backend to Flask.

How to test:
Setup annotation engine locally (follow setup.md).

1. View the progress bars for each batch and word in batch selection page and top of annotation pages.
2. Press "View Summary" button on annotation pages. Should see labeled and unlabeled videos summarized.
3. View "Resume Where You Left Off" card at the top of the batch selection page that allows you to jump to your last annotated video and see summary page.

Expected results:
Progress bars, summary page, resume where you left off button all functional.

Batch/word progress bars and resume where you left off card:

Summary page:

Word progress bar and view summary button:

Sections written with AI assistance:

WebAnnotationEngine/src/routes/+layout.svelte:
28

WebAnnotationEngine/src/routes/annotation/[batch]/[word]/+page.svelte
22-52
96-97
250-262

flask_app/batches.py:
26-138 (get_batches())

flask_app/videos.py:
15-45 (_send_with_range())

[bzhang625]

Hi!, I'll edit the PR message with info regarding what parts we used AI for by the next VIP meeting!

[wcn4]

Currently on Chrome and Safari when I am testing, I am currently getting this error:

I believe this may be a CORS related issue. I tried looking into it for about 2 hours but I am not sure currently what needs to be modified to get these features to work.

I was able to get it to work on Firefox, and from what I was able to test and see it looks good:

If you are able to reproduce and identify the source of this bug, I will be happy to rereview.

Since we are no longer using a svelte based backend, we should the config from WebAnnotationEngine static files to the flask_app (be sure to update the gitignore accordingly).