Add channel headers to Sequencer

There are a lot of functions in the Sequencer with no UI elements. Channel controls are some of them, but actually, that UI header functionality is already in the Dope Sheet in Blender, so this suggestion is to reuse the Dope Sheet channel header UI code for some new Sequencer Channel headers with ex. a title, hide, mute and lock and with the triangle icon, the Meta strips could also be opened and collapsed. An illustration: