(split from main repo) Move common references into Directory.Build.props

* System
* System.ComponentModel.Composition
* System.Drawing
* System.Windows.Forms
* netstandard

Author: RussKie

Gerrit.csproj

@@ -1,11 +1,4 @@
 <Project Sdk="Microsoft.NET.Sdk">
-  <ItemGroup>
-    <Reference Include="System" />
-    <Reference Include="System.ComponentModel.Composition" />
-    <Reference Include="System.Drawing" />
-    <Reference Include="System.Windows.Forms" />
-    <Reference Include="netstandard" />
-  </ItemGroup>
 
   <ItemGroup>
     <PackageReference Include="Newtonsoft.Json" Version="10.0.3" />