tmux: Present itself as a screen-256color terminal

Tmux likes when the TERM variable is set to "screen-256color" so we set
it as so in the Tmux configuration file. This way it can set the
variable for itself when it starts and we do not need to change the
environment when Tmux is not running.

Signed-off-by: Henrique Camargo <henrique@henriquecamargo.com>
tmux: Change the color of the status bar

Change the color of the status bar to yet another shade of orange. I
think this is closer to the overall Ubuntu look.

Signed-off-by: Henrique Camargo <henrique@henriquecamargo.com>
bash: Don't set TERM to screen-256color

Setting the TERM variable to screen-256color in the bashrc file was a
hack to get 256 color support inside Tmux.

Tmux works best when the TERM is set to screen-256color. Unfortunately
with this setting, the combination of gnome-terminal and vim display
weird behaviours when the END or HOME keys are pressed. When END is
pressed an empty line with an F appears, and when HOME is pressed an
empty line with an H appears. So clearly bashrc is not the best place to
set the TERM variable to screen-256color.

Signed-off-by: Henrique Camargo <henrique@henriquecamargo.com>
bash: Set the TERM variable to xterm-256color

This is a hack to fix the TERM variable set by gnome-terminal, this is
not the correct place to set the TERM variable but gnome-terminal sets
it to xterm even though it supports 256 colors with xterm-256color. I
needed to force it somewhere and this was the place chosen.

Signed-off-by: Henrique Camargo <henrique@henriquecamargo.com>