Added configuration for tmux (http://tmux.sourceforge.net/)

This configuration is a copy of the one developed by Brian P. Hogan in
his book "tmux - Productive Mouse-Free Development"
Adjusted some tmux-settings

- removed battery, date and time from status (this is already covered by
  xmobar)
- changed location of optional log file
- use zsh as default shell
Increased number of CPUs
Added new floating applications and experimental changes