Use blithely correctly

Thanks to Matthew Emerton
http://stacks.math.columbia.edu/tag/0AHY#comment-1010
Move definition skelet functors earlier

Thanks to correction_bot
http://stacks.math.columbia.edu/tag/017F#comment-1015
Composition of strict morphisms isn't strict

Thanks to JuanPablo
The counter example given is due to JuanPableo
http://stacks.math.columbia.edu/tag/05SJ#comment-1011
Changes thanks to correction_bot

Thanks to correction_bot
http://stacks.math.columbia.edu/tag/01G6#comment-1025