Update greetings.txt

was suggested on the irc
Merge branch 'patch-2' of https://github.com/JoshTheEnder/OpenComputers
Cleaned up greetings.txt some more (duplicates, typos, out-of-date stuff).
Little bit of refactoring and showing the tier of item components in their tooltip if advanced tooltips are enabled (F3+H), for people that have problems distinguishing the tier by color (e.g. colorblind people).
Fixed potential NPE in server rack (since: sided fix for internal switch mode).
Merge branch 'OC1.3-MC1.6.4' of github.com:MightyPirates/OpenComputers