Mute warnings about obsolete code

We have a ton of code marked with [Obsolete]
and no dependencies beyond .NET framework so we will likely
not run into using code ourselves marked Obsolete. Mute this globally
for now, we can later consider muting each usage instead but right now
that would really pollute the code.

Mute warning CS0618 usage of obsolete member
Mute warning CS0809 obsolete member overrides non-obsolete member

Author: angularsen

UnitsNet.Serialization.JsonNet/UnitsNet.Serialization.JsonNet.Common.props

@@ -25,6 +25,7 @@
     <FrameworkPathOverride Condition="'$(TargetFramework)' == 'net35'">C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v3.5\Profile\Client</FrameworkPathOverride>
     <BaseIntermediateOutputPath>obj\$(MSBuildProjectName)</BaseIntermediateOutputPath>
     <OutputPath>..\Artifacts\$(MSBuildProjectName)</OutputPath>
+    <NoWarn>CS0618</NoWarn>
   </PropertyGroup>
   <!-- NuGet references that work for both signed and unsigned -->
   <ItemGroup>

UnitsNet.Tests/UnitsNet.Tests.csproj

@@ -4,6 +4,7 @@
     <TargetFrameworks>netcoreapp1.1</TargetFrameworks>
     <RootNamespace>UnitsNet.Tests</RootNamespace>
     <OutputPath>..\Artifacts\$(MSBuildProjectName)</OutputPath>
+    <NoWarn>CS0618</NoWarn>
   </PropertyGroup>
 
   <ItemGroup>

UnitsNet/UnitsNet.Common.props

@@ -26,6 +26,7 @@
     <RootNamespace>UnitsNet</RootNamespace>
     <!-- Workaround for building with dotnet CLI and targeting .NET 3.5: https://github.com/Microsoft/msbuild/issues/1333#issuecomment-296346352 -->
     <FrameworkPathOverride Condition="'$(TargetFramework)' == 'net35'">C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v3.5\Profile\Client</FrameworkPathOverride>
+    <NoWarn>CS0618,CS0809</NoWarn>
   </PropertyGroup>
 
   <!-- NuGet references that work for both signed and unsigned -->