migrate to newer signing infra with snk

- folks can now build a release/debug build without having a key
  locally.
- when we want to publish a release that has been signed you can use:
  `-p:SignAssemblies=True`.
  - I know you already have a PFX file, so you'll need to convert it to
    a strongnamekey (there are lots of tools for this online, but if you
    need any help let me know).

.gitignore

@@ -242,7 +242,7 @@ orleans.codegen.cs
 
 # Including strong name files can present a security risk
 # (https://github.com/github/gitignore/pull/2483#issue-259490424)
-#*.snk
+*.snk
 
 # Since there are multiple workflows, uncomment next line to ignore bower_components
 # (https://github.com/github/gitignore/pull/1529#issuecomment-104372622)

AC_e-Reader_Card_Creator/AC_e-Reader_Card_Creator.csproj

@@ -24,13 +24,12 @@
     <ImportWindowsDesktopTargets>true</ImportWindowsDesktopTargets>
   </PropertyGroup>
 
-  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
-    <ManifestCertificateThumbprint>8C26734D6AC4E12062A9F4AF2B1C64330FB784B2</ManifestCertificateThumbprint>
-    <ManifestKeyFile>AC_e-Reader_Card_Creator_TemporaryKey.pfx</ManifestKeyFile>
+  <PropertyGroup Condition="'$(SignAssemblies)' == 'True'">
+    <AssemblyOriginatorKeyFile>AC_e-Reader_Card_Creator_TemporaryKey.snk</AssemblyOriginatorKeyFile>
     <SignManifests>true</SignManifests>
   </PropertyGroup>
-  <ItemGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
-    <None Include="AC_e-Reader_Card_Creator_TemporaryKey.pfx" />
+  <ItemGroup Condition="'$(SignAssemblies)' == 'True'">
+    <None Include="AC_e-Reader_Card_Creator_TemporaryKey.snk" />
   </ItemGroup>
 
   <PropertyGroup>