Improve SSH autocompletion

Only autocomplete when known hosts file is available
Autocomplete also for scp and sftp
Add afk alias to put system into suspend mode

Useful when the screensaver has a password set
Increase bash history size
Improve bash autocompletion

Show auto-completion on first tab (default is second tab).
disable empty command completion
show only dirs on cd and rmdir autocomplete
add better completition for killall