Re-enable Esc key in Vim, and fix a typo

Since <Esc> being disabled is so non-standard, and I occasionally have
to switch to machines that don't have it disabled (and also don't have
my custom `jk`-to-escape mapping) it makes more sense to leave it
enabled - I have learned not to use it by default, but if I have to
toggle that switch in my brain and go between a machine with it and a
machine without it frequently, it doesn't completely melt my head.
Update some Vim PostgreSQL interactions

Sometimes I write `DO` statements into my SQL files as part of
migrations or simply when using "vim-slime" to edit large and
complicated queries in another tmux pane, and so it's helpful to have
the code highlighted properly for PLPERL in this case as well, and not
just function definitions.

The other update changes the mapping for sending a PostgreSQL query in
the background to prefix it with the <Leader> key. This command wasn't
in my memory very deeply and it's very uncommon that I use it, so I
figure it doesn't need to be overwriting any built-in commands like
that, when this sort of thing is precisely what <Leader> is useful for.
Add simple paste mode toggle in Vim