Private Email Service Support (#1028)

* Added ServerSettingKey's for SMTP and moved email service code to Kavita. Nothing integrated in the UI yet.

* Undo all the custom SMTP stuff and prepare for custom email service url.

* Foundation for email service to use a custom url is setup.

* Implemented the ability to hook up custom email url

API/API.csproj

@@ -101,6 +101,9 @@
     <Compile Remove="logs\**" />
     <Compile Remove="temp\**" />
     <Compile Remove="covers\**" />
+    <Compile Remove="DTOs\Email\SmtpConfig.cs" />
+    <Compile Remove="DTOs\Email\EmailOptionsDto.cs" />
+    <Compile Remove="Helpers\Converters\SmtpConverter.cs" />
   </ItemGroup>
 
   <ItemGroup>