A user can delete posts

Added logic to verify user who created post is the only one that can
see Delete link (didn't actually verify that logic worked)
Shout outs to Ifeanyi for holding my hand while I cried over instance variables

:-1: boo hiss, pull this into a method on user. Maybe something like

`<% if current_user.owns?(post) %>` or `<% if current_user.can_edit?(post) %>`