Added slides for Lesson 9 of Module 1, "Subnetting IP Networks"

These slides are almost completely rewritten from scratch and reorganized, compared to last year's, except for IPv6 subnetting.
Examples completely reworked, for now in-slide exercises are removed.
Added slides for Lesson 10 of Module 1, "Application Layer"

These slides are a more thorough revision of last year's, and add the missing part about the more common application layer protocols (HTTP, POP, IMAP, SMTP, FTP, SMB).