Auto detect used C# libraries

When using `mcs` on Fedora, ALE doesn't detect used assemblies and requires them to be added manually, such as `System.Net.Http` in the example below. Is would be nice if ALE could detect those and do not fail with the error.

```csharp
using System;
using System.Net.Http;

class Program
{
>> static HttpClient Client = new HttpClient();

static void Main(string[] args)
{

var hyper = "inter";
Console.WriteLine($"string {hyper}polation");
}
}
~
~
~
CS0246: The type or namespace name `HttpClient' could not be found. Are you missing an assembly reference?
```