Merge pull request #185 from AY2324S2-CS2103T-W12-3/update-copyright-…

…notice

Update copyright notice

copyright.txt

@@ -1,9 +1,5 @@
 Some code adapted from http://code.makery.ch/library/javafx-8-tutorial/ by Marco Jakob
+AssetBook icon designed using icons from UXWing - https://uxwing.com/
 
-Copyright by Susumu Yoshida - http://www.mcdodesign.com/
-- address_book_32.png
-- AddressApp.ico
-
-Copyright by Jan Jan Kovařík - http://glyphicons.com/
-- calendar.png
-- edit.png
+Copyright by The JetBrains Mono Project Authors - https://github.com/JetBrains/JetBrainsMono
+- JetBrainsMono-SemiBold.ttf