Dynamic window and tab title

## Problem
The window or tab title only show the current directory. For me is not possible to see, which user use this terminal (user or root). Some commands like emerge, apt-get or pacman need to change the title to see the progress.

## Proposal
Please add a dynamic title like username@hostname:currentdirectory. If i am the user which start the terminal the nicer way should be to see only username@hostname:~/Downloads in the title. If i switch so root the full path should be shown like root@hostname:/home/username/Downloads
Some commands like emerge or pacman should be allow to change the title dynamic. So i am able the progress of this commands.
Please take a look to the mate-terminal.