Is your feature request related to a problem? Please describe.
It would be great if there is a bookmark button on each target, and the bookmarked targets can be reviewed later.

Describe the solution you'd like
There can be a bookmark page on the main website, which may contain bookmarks for all the courses. Each bookmarked target and/or exercise can be easily accessed from there.
For

• Разнести админку из admin.py по отдельным файлам
• Разнести модели из models.py по отдельным файлам

Reproduction Steps

Go to Orders >> Orders
Try to search for an order number.

Expected Behavior

The search result should come up with the order number as first and the closely related numbers for others.

Actual Behavior

It doesn't search for the order using order number

Error Messages / Logs

• Include any relevant error messages or log files

N/A

The most recent full CI build (at the time of this writing) failed due to connection refused, but it was just transient (manually browsed the site and confirmed it worked). We should add some retries to the full CI's smoke test code so that these transient failures wouldn't cause full CI failures. Relevant code is [here](https://github.com/Azu