[vim] disable execution of modelines

Modelines can be quite annoying or even dangerous, even though the
commands that can be executed int them are limited. If the settings from
a modeline are actually desired, this can be explicitly enabled on a
per-file basis.

vimrc

@@ -23,6 +23,7 @@ set nocompatible
     set   laststatus=2
     set   lazyredraw
     set   listchars=tab:›\ ,trail:·
+    set   modelines=0
     set   number
     set   scrolloff=5
     set   shiftwidth=4