Split Modification class functionality

This had the potential to cause a lot of issues the way it was. Moving the actual functionality for cleaning, filtering, and applying extras to their appropriate classes allows for less redirection when calling into the code. Modification as a class was essentially a shell around things that should have just been a single call.

SabreTools.Filtering/DatHeaderRemover.cs

@@ -33,7 +33,7 @@ namespace SabreTools.Filtering
 
         #endregion
 
-        #region Remover Population
+        #region Population
 
         /// <inheritdoc/>
         public override bool SetRemover(string field)
@@ -55,7 +55,7 @@ namespace SabreTools.Filtering
 
         #endregion
 
-        #region Remover Running
+        #region Running
 
         /// <summary>
         /// Remove fields with given values