Change namespace to Jackett.Common (#2691)

Really hope I don't break anything with this
Went to have a go at .NET core and it just became too confusing for me with 'Jackett' namespace referring to both Jackett.Common and Jackett

src/Jackett.Common/Utils/ParseUtil.cs

@@ -1,10 +1,9 @@
 using System.Globalization;
 using System.Linq;
 using System.Text.RegularExpressions;
-using System.Web;
 using Microsoft.AspNetCore.WebUtilities;
 
-namespace Jackett.Utils
+namespace Jackett.Common.Utils
 {
     public static class ParseUtil
     {