Add option to avoid drag & drop timeline range from edges

Related to #1498 in some way to start enabling new selection modes in
the timeline.

data/pref.xml

@@ -204,6 +204,7 @@
       <option id="select_on_click" type="bool" default="false" />
       <option id="select_on_click_with_key" type="bool" default="true" />
       <option id="select_on_drag" type="bool" default="true" />
+      <option id="drag_and_drop_from_edges" type="bool" default="true" />
     </section>
     <section id="cursor">
       <option id="use_native_cursor" type="bool" default="false" />

data/strings/en.ini

@@ -1677,6 +1677,7 @@ Enable the selected range of layers/frames/cels
 when we press the mouse button and after we move
 the mouse to another position.
 END
+drag_and_drop_from_edges = Drag && drop from edges
 reset_as_v12 = Reset as Aseprite v1.2
 default_first_frame = Default First Frame:
 ui_mouse_cursor = UI Mouse Cursor

data/widgets/options.xml

@@ -295,6 +295,9 @@
                  text="@.select_on_drag"
                  tooltip="@.select_on_drag_tooltip"
                  pref="timeline.select_on_drag" />
+          <check id="drag_and_drop_from_edges"
+                 text="@.drag_and_drop_from_edges"
+                 pref="timeline.drag_and_drop_from_edges" />
           <hbox>
             <hbox expansive="true" />
             <button id="reset_timeline_sel" text="@general.reset" width="60" />

src/app/commands/cmd_options.cpp

@@ -1701,18 +1701,21 @@ private:
     layout();
   }
 
-  void onResetTimelineSel() {
+  void onResetTimelineSelCommon() {
     keepSelection()->setSelected(false);
-    selectOnClick()->setSelected(false);
     selectOnClickWithKey()->setSelected(true);
     selectOnDrag()->setSelected(true);
+    dragAndDropFromEdges()->setSelected(true);
+  }
+
+  void onResetTimelineSel() {
+    onResetTimelineSelCommon();
+    selectOnClick()->setSelected(false);
   }
 
   void onResetTimelineSelV12() {
-    keepSelection()->setSelected(false);
+    onResetTimelineSelCommon();
     selectOnClick()->setSelected(true);
-    selectOnClickWithKey()->setSelected(true);
-    selectOnDrag()->setSelected(true);
   }
 
   gfx::Rect gridBounds() const {

src/app/ui/timeline/timeline.cpp

@@ -3529,7 +3529,8 @@ Timeline::Hit Timeline::hitTest(ui::Message* msg, const gfx::Point& mousePos)
              mouseMsg &&
              mouseMsg->right()) ||
             // Drag with left-click only if we are inside the range edges
-            !gfx::Rect(outline).shrink(2*outlineWidth()).contains(mousePos)) {
+            (Preferences::instance().timeline.dragAndDropFromEdges() &&
+             !gfx::Rect(outline).shrink(2*outlineWidth()).contains(mousePos))) {
           hit.part = PART_RANGE_OUTLINE;
         }
       }