Gooseberry animation request: Paste flipped pose in action

and graph editor.

This was a tricky commit that was not so straightforward to make work.
The information for bones is not easy to come by in the animation curves,
however we do have some string manipulation tricks to make it happen.

Testing in gooseberry worked for the rigs there, commiting to master now

release/scripts/startup/bl_ui/space_dopesheet.py

@@ -131,6 +131,8 @@ class DOPESHEET_HT_header(Header):
         row = layout.row(align=True)
         row.operator("action.copy", text="", icon='COPYDOWN')
         row.operator("action.paste", text="", icon='PASTEDOWN')
+        row.operator("action.paste", text="", icon='PASTEFLIPDOWN').flipped = True
+
 
 
 class DOPESHEET_MT_editor_menus(Menu):

release/scripts/startup/bl_ui/space_graph.py

@@ -52,6 +52,7 @@ class GRAPH_HT_header(Header):
         row = layout.row(align=True)
         row.operator("graph.copy", text="", icon='COPYDOWN')
         row.operator("graph.paste", text="", icon='PASTEDOWN')
+        row.operator("graph.paste", text="", icon='PASTEFLIPDOWN').flipped = True
 
         row = layout.row(align=True)
         if st.has_ghost_curves: