Rename breakOnUnsupportedCmds to throwOnError.

Also, the MathBb-chrome test changed, to what I believe is the correct
result? Not sure why it looked wrong before.

Test plan:
 - `make test`
 - take screenshots, see nothing changed.

src/Settings.js

@@ -21,7 +21,7 @@ function Settings(options) {
     // allow null options
     options = options || {};
     this.displayMode = get(options.displayMode, false);
-    this.breakOnUnsupportedCmds = get(options.breakOnUnsupportedCmds, true);
+    this.throwOnError = get(options.throwOnError, true);
     this.errorColor = get(options.errorColor, "#cc0000");
 }