Make it possible to play The Shivah: Kosher Edition

This implements enough of the agswadjetutil plugin for me to successfully play The Shivah: Kosher Edition (GoG.com version) under Linux. Actually, the only function I ever saw being called was the IsOnPhone() one, so the remaining ones are just untested stubs. I don't even know if they take the appropriate data types for their parameters. There are also some things I've simply cut and pasted, since I don't have the hardware to build it. And since I'm very unfamiliar with AGS, it's probably safest to assume that if there are problems with it, I'm not the right person to fix them.

So yeah, it's not meant as a final version but perhaps something to build a final version from. It would be a shame if the game wasn't playable because of something as trivial as this.