This patch will add support to select all channels between active channel and last-clicked channel without deselecting previous selection. `Shift` key is now assigned for the range selection and `ctrl` key to extend the selection. This changes will make multi-selection similar as outliner tree-elements. New function is created `animchannel_select_range` to handle the range selection of channels. Old Differential revision: https://archive.blender.org/developer/D17079 Pull Request: blender/blender#104565