Minor cleanup

Remove left/right arrow PNGs.  Remove duplicate copies of icon.
Tweak some comments.  Set application icon.  Adjust padding on
group boxes in first tab of app settings.

SourceGen/SourceGen.csproj

@@ -34,6 +34,9 @@
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
+  <PropertyGroup>
+    <ApplicationIcon>Res\SourceGenIcon.ico</ApplicationIcon>
+  </PropertyGroup>
   <ItemGroup>
     <Reference Include="System" />
     <Reference Include="System.Data" />