Popup window to show current status

[jiin-kim109]

Description:
As a product owner, I would like to see a popup window that shows whether the extension is in initialization processing, or is ready to show RMP rating in SFU pages.

The popup window should show "In progress" graphic when the extension is browsing for available SFU programs and course sessions in the current semester.

After it's done, the extension should show a check icon or confirmation image, and the timestamp of the last update. On a regular basis the extension should clear caches and update programs and course sessions.

Acceptance Criteria:

1. Manually check if the popup window shows clear UI when the extension is in initialization process, or is running for update.
2. Manually check if the popup window shows clear UI when the extension is ready to show RMP ratings.
3. Write sufficient test scenarios for the cases when the extension isn't ready, is ready, is running for update.