Adding "OptionNames" in SyntaxInformation of WolframModelPlot. (#454)

## Changes
* Closes #218.
* Adding "OptionNames" in `SyntaxInformation` of `WolframModelPlot`.

## Examples
```wl
In[] := WolframModelPlot[{{1, 2, 3}}, "InvalidOption" -> 4]
```
![image](https://user-images.githubusercontent.com/40190339/95776857-c0869e00-0c8a-11eb-93e7-74b8df0853b0.png)

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Kernel/WolframModelPlot.m

@@ -12,8 +12,6 @@
 WolframModelPlot::usage = usageString[
   "WolframModelPlot[`s`, `opts`] plots a list of vertex lists `s` as a hypergraph."];
 
-SyntaxInformation[WolframModelPlot] = {"ArgumentsPattern" -> {_, _., OptionsPattern[]}};
-
 $plotStyleAutomatic = <|
   $vertexPoint -> style[$lightTheme][$vertexStyle],
   $edgeLine -> style[$lightTheme][$edgeLineStyle],
@@ -41,6 +39,10 @@
 
 Options[WolframModelPlot] = Join[$newOptions, $defaultGraphicsOptions];
 
+SyntaxInformation[WolframModelPlot] = {
+  "ArgumentsPattern" -> {_, _., OptionsPattern[]},
+  "OptionNames" -> Options[WolframModelPlot][[All, 1]]};
+
 $edgeTypes = {"Ordered", "Cyclic"};
 $defaultEdgeType = "Ordered";
 $graphLayout = "SpringElectricalEmbedding";