#768 Add support for global scriptcs.opts file

FileSystem.GlobalOptsFile will return the path for a scriptcs.opts file
in the ModulesFolder

ArgumentHandler looks for non-default option values first from the
command line, then from a local opts file if it exists, and finally from
a global opts file if it exists.
this filename is hardcoded now in 3 places - `ScriptCsArgs`, `ArgumentHandler` and here - do you mind adding a constant?