first-parent-filter

need help in two issues:
1. use better icon - I just reused the Filter icon
2. lines of merge commits are still rendered - need to skip them since they don't link to any commit when filter enabled. I didn't manage to solve by my own right now

src/Models/RepositorySettings.cs

@@ -70,6 +70,12 @@ namespace SourceGit.Models
             set;
         } = false;
 
+        public bool FirstParentFilterEnabled
+        {
+            get;
+            set;
+        } = false;
+
         public AvaloniaList<string> Filters
         {
             get;