[TMUX] Update config for v2.1
[TMUX] Update config for v2.1

Most recent versions of Ubuntu (since 16.04) provides a more rencent
version of tmux (v2.1) where certain options have been removed or
changed.

This patch updates my configuration accoding to tips and notes recovered
from this page:
   https://www.reddit.com/r/tmux/comments/3paqoi/tmux_21_has_been_released/cw552qd

Specifically:
- update mouse mode and add new bindings for PageUp/PageDown and scroll
  wheel to enter/exit copy mode
- remove c0-* options which are not more supported/required

Signed-off-by: Patrick Bellasi <431c86f368affbc3148c4669fbd465131f7e82cb@arm.com>

derkling/dotfiles,derkling/dotfiles,derkling/dotfiles,derkling/dotfiles