Currently we expect the user to do everything by left-clicking: selecting elements, dragging them, trimming them, seeking .
- Right-click should be seek-only.
- Left-click should optionally select/edit-only, without seeking.
This is similar with how Blender's video timeline works. Left click is for seeking only and right click is for selecting elements. We'd have it the other way around, since normally in a Gtk app you drag&drop with the left mouse button.
Imported from https://bugzilla.gnome.org/show_bug.cgi?id=724751