EXT-7532 FIXED (Improve discoverability of sidebar Back button)

- New art was added in the textures.xml.
- New art was applied to the back button in the following panels:

  panel_profile_view.xml
  panel_block_list_sidetray.xml
  panel_classified_info.xml
  panel_edit_classified.xml
  panel_pick_info.xml
  panel_edit_pick.xml
  panel_edit_wearable.xml
  panel_group_info_sidetray.xml
  panel_landmark_info.xml
  panel_outfit_edit.xml
  panel_place_profile.xml
  sidepanel_item_info.xml

  Reviewed by Vadim Savchuk at https://codereview.productengine.com/secondlife/r/487/

--HG--
branch : product-engine