Tmux: cosmetic changes with new utf-8 symbols

* Add utf-8 symbols for date.
* Change 'R' utf-8 symbol to left most side.
* Add utf-8 symbol 'D' for date


Signed-off-by: Ratheesh S <ratheeshreddy@gmail.com>
Tested-by: Ratheesh S <ratheeshreddy@gmail.com>