update how theme files are copied to output folder

Moved the copying of themes from the build script to the project file.
The recursive copy-item call in the post-build script was causing the
2 files inside `Themes/ThemeBuilder` to also be copied, which resulted
in the `Tempalte.xaml` being loaded at runtime as a theme.

Closes #38

Flow.Launcher/Flow.Launcher.csproj

@@ -62,6 +62,14 @@
     </Content>
   </ItemGroup>
 
+  <ItemGroup>
+    <Content Include="Themes\*.xaml">
+      <Generator>MSBuild:Compile</Generator>
+      <SubType>Designer</SubType>
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </Content>
+  </ItemGroup>
+
   <ItemGroup>
     <PackageReference Include="InputSimulator" Version="1.0.4" />
     <PackageReference Include="JetBrains.Annotations" Version="2019.1.3" />

Scripts/post_build.ps1

@@ -35,7 +35,6 @@ function Copy-Resources ($path, $config) {
     $project = "$path\Flow.Launcher"
     $output = "$path\Output"
     $target = "$output\$config"
-    Copy-Item -Recurse -Force $project\Themes\* $target\Themes\
     Copy-Item -Recurse -Force $project\Images\* $target\Images\
     Copy-Item -Recurse -Force $path\Plugins\HelloWorldPython $target\Plugins\HelloWorldPython
     Copy-Item -Recurse -Force $path\JsonRPC $target\JsonRPC