common: include "less" as an essential tool

It used to be pulled in as a dependency of gzip, but that was recently
changed to an optional dependency [1]. It's a good tool so add it back.

[1] archlinux/packaging/packages/gzip@be440e27

roles/common/tasks/main.yml

 - name: Install essential tools
-  pacman: name=vim,nano,tmux,htop,ncdu,bash-completion,rsync,vnstat state=present
+  pacman: name=less,vim,nano,tmux,htop,ncdu,bash-completion,rsync,vnstat state=present
 
 - name: Install compsize for use with btrfs
   pacman: name=compsize state=present