Introduce -d flag to set the compression level of the ISO ...

No write access here 😜 .. BTW this commit introduce -d flag : i have reintroduce the possibility to set the compression level during squash process of the ISO.. Now we can set example buildiso -p gnome -d lz4 to decrease the squash process.. The default value is xz. We can also set the default value in the manjaro-tools.conf file .

In our forum i have see this request and in my POV make sense .. also because in any case the value is xz