IPC services refactoring (#726)

* IPC services refactoring

- Use custom Attributes to handle services.
- Add a way to set the permissions and fix the bsd service to use it.
- Little cleanup.
- C#7.1 is required.

* fix var name

* fix syntax

* Change Permission to Parameter

* Delete BsdServicePermissionLevel.cs

* Fix Linq

Ryujinx.HLE/Ryujinx.HLE.csproj

@@ -4,6 +4,7 @@
     <TargetFramework>netcoreapp2.1</TargetFramework>
     <RuntimeIdentifiers>win10-x64;osx-x64;linux-x64</RuntimeIdentifiers>
     <Configurations>Debug;Release;Profile Debug;Profile Release</Configurations>
+    <LangVersion>7.1</LangVersion>
   </PropertyGroup>
 
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|AnyCPU'">