(GH-79) Use embedded icon for nuget package

resolves #79

.gitmodules

@@ -0,0 +1,4 @@
+[submodule "graphics/cake-contrib"]
+    path = graphics/cake-contrib
+    url = https://github.com/cake-contrib/graphics.git
+    branch = master

src/Cake.Transifex/Cake.Transifex.csproj

@@ -20,6 +20,7 @@ To install the transifex client, install python, then run `pip install transifex
     <Authors>Kim J. Nordmo;$(Company)</Authors>
     <IncludeSymbols>true</IncludeSymbols>
     <SymbolPackageFormat>snupkg</SymbolPackageFormat>
+    <PackageIcon>cake-contrib-small.png</PackageIcon>
     <PackageIconUrl>https://cdn.jsdelivr.net/gh/cake-contrib/graphics@49c3b71def749b86416d773f1ead0c0da2d590ea/png/cake-contrib-medium.png</PackageIconUrl>
     <PackageLicenseExpression>MIT</PackageLicenseExpression>
     <PackageProjectUrl>https://cake-contrib.github.io/Cake.Transifex/</PackageProjectUrl>
@@ -37,6 +38,13 @@ To install the transifex client, install python, then run `pip install transifex
     <PackageReference Include="Cake.Core" Version="0.33.0" PrivateAssets="All" />
   </ItemGroup>
 
+  <ItemGroup>
+    <None Include="..\..\graphics\cake-contrib\png\cake-contrib-small.png">
+      <Pack>True</Pack>
+      <PackagePath></PackagePath>
+    </None>
+  </ItemGroup>
+
   <ItemGroup>
     <Compile Update="Common.Designer.cs">
       <DesignTime>True</DesignTime>