Added settings window to configure which shell to use

FluentTerminal.Models/ShellConfiguration.cs

@@ -0,0 +1,12 @@
+using FluentTerminal.Models.Enums;
+
+namespace FluentTerminal.Models
+{
+    public class ShellConfiguration
+    {
+        public string Arguments { get; set; }
+        public ShellType Shell { get; set; }
+        public string CustomShellLocation { get; set; }
+        public string WorkingDirectory { get; set; }
+    }
+}