Urls and Response Headers

• Fixed Feed and Sitemap urls
• Added extra Response Headers, making it graded "A" on https://securityheaders.com

Small fixes

• Fixed merge issues
• Updated packages
• Sync branches

Upgraded to .NET Core 3.0

• Upgraded .NET Core from 2.2 to 3.0
• Improved the architecture of the project
• A lot of refactoring was done
• Added some new functionality (i.e.: Contact form)