Prefer "Count" to "Count()"

If it is an `IList` or some other object that has `Count` as a property, don't use the Linq extension method.

So this:

``` csharp
var count = myList.Count();
```

Becomes:

``` csharp
var count = myList.Count;
```

**Important**:
`Count` and `Count()` have to return the same type.
`Count()` has to be an extension method.

Diagnostic id: `CC0098`
Severity: Warning
Category: Performance
