FileManager: Move the main window UI to GML

This was pretty straightforward although it does expose a bunch of
missing functionality (mostly properties.)

Applications/FileManager/FileManagerWindow.gml

@@ -0,0 +1,54 @@
+@GUI::Widget {
+    fill_with_background_color: true
+    layout: @GUI::VerticalBoxLayout {
+        spacing: 2
+    }
+
+    @GUI::ToolBarContainer {
+        @GUI::ToolBar {
+            name: "main_toolbar"
+        }
+        @GUI::ToolBar {
+            name: "location_toolbar"
+            visible: false
+
+            @GUI::Label {
+                name: "location_label"
+                text: "Location: "
+            }
+
+            @GUI::TextBox {
+                name: "location_textbox"
+                vertical_size_policy: "Fixed"
+                preferred_height: 22
+            }
+        }
+        @GUI::ToolBar {
+            name: "breadcrumb_toolbar"
+
+            @GUI::BreadcrumbBar {
+                name: "breadcrumb_bar"
+            }
+        }
+    }
+
+    @GUI::HorizontalSplitter {
+        name: "splitter"
+
+        @GUI::TreeView {
+            name: "tree_view"
+            horizontal_size_policy: "Fixed"
+            preferred_width: 175
+        }
+
+    }
+
+    @GUI::StatusBar {
+        name: "statusbar"
+
+        @GUI::ProgressBar {
+            name: "progressbar"
+            visible: false
+        }
+    }
+}