MainPage, Registration, and Login Classes modified

MainPage Changes

• Fixed light and dark mode inconsistency when it comes to text/Labels not updating properly when modes switch. For example, if in dark mode, the texts stays as colour gray which makes it hard to read.
• Reformated profile/setting button (top left)
  • Should now display employee info as well
  • User can log out from that window also
  • Added an image to the circle button
• Extracted methods to avoid duplication

Registration and Login Changes:

• Added background colours
• Change text colours

Deleted unused ProfileCircle.java