Use Directory.Build.props for common settings

Directory.Build.props

@@ -0,0 +1,9 @@
+<Project>
+
+  <PropertyGroup>
+    <TargetFramework>net35</TargetFramework>
+    <LangVersion>9</LangVersion>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+  </PropertyGroup>
+
+</Project>

src/MeidoPhotoStudio.Converter/MeidoPhotoStudio.Converter.csproj

@@ -1,8 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFramework>net35</TargetFramework>
     <ProjectGuid>{19D28B0C-3537-4FEE-B7B3-1ABF70B16D5E}</ProjectGuid>
-    <LangVersion>9</LangVersion>
     <Nullable>enable</Nullable>
   </PropertyGroup>
   <ItemGroup>

src/MeidoPhotoStudio.Plugin/MeidoPhotoStudio.Plugin.csproj

@@ -1,8 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
     <PropertyGroup>
-        <TargetFramework>net35</TargetFramework>
-        <LangVersion>9</LangVersion>
-        <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
         <Configurations>Debug;Release</Configurations>
         <Platforms>AnyCPU</Platforms>
     </PropertyGroup>