Remove Math.abs

Slightly simplified the code - no functional changes.
Switch from local storage to account storage

Using chrome.storage.sync allows storage of data for the user, not for
the computer. Also, a function was created to get the student ID. It was
made because I plan to be able to distinguish between grades of
different IDs.
Update version

Updated from 1 to 1.1, and also added a short name ("Grade Checker")
add readme