nixos/vte: init

This module correctly includes the vte.sh script
required for vte terminals like gnome-terminal to show the
CWD in the window title and preserved across instances.

This is achieved with the options:
* programs.bash.vteIntegration
* programs.zsh.vteIntegration

as it's best to keep this configuration unguarded by gnome3.enable
to support other vte terminals (such as elementary-terminal).
Note the distinction between Zsh and Bash doesn't include
a different script, as this script only supports those two shells.