UI: allow to hide markers region per editor

Instead of having the option to show marker lines,
make the marker region optional.

- Added a Show Markers entry in the View menu of the animation editors.
- If the markers region is not active then the Marker menu gets hidden.
- Removed marker menu from the driver editor
  and don't allow to use marker operators.

release/scripts/startup/bl_ui/space_nla.py

@@ -71,10 +71,12 @@ class NLA_MT_editor_menus(Menu):
     bl_label = ""
 
     def draw(self, _context):
+        st = _context.space_data
         layout = self.layout
         layout.menu("NLA_MT_view")
         layout.menu("NLA_MT_select")
-        layout.menu("NLA_MT_marker")
+        if st.show_markers:
+            layout.menu("NLA_MT_marker")
         layout.menu("NLA_MT_edit")
         layout.menu("NLA_MT_add")
 
@@ -96,8 +98,10 @@ class NLA_MT_view(Menu):
         layout.prop(st, "show_locked_time")
 
         layout.prop(st, "show_strip_curves")
+
+        layout.separator()
+        layout.prop(st, "show_markers")
         layout.prop(st, "show_local_markers")
-        layout.prop(st, "show_marker_lines")
 
         layout.separator()
         layout.operator("anim.previewrange_set")