Emacs: Add melpa-stable for package management

Signed-off-by: Ratheesh S <ratheesh@mistralsolutions.com>
Tested-by: Ratheesh S <ratheesh@mistralsolutions.com>
Configure swoop package

Signed-off-by: Ratheesh S <ratheesh@mistralsolutions.com>
Tested-by: Ratheesh S <ratheesh@mistralsolutions.com>
Emacs: disable obsolete iswitchb package

Signed-off-by: Ratheesh S <ratheesh@mistralsolutions.com>
Tested-by: Ratheesh S <ratheesh@mistralsolutions.com>
tmux: Change powerline version