[MlMt] Easy way to auto-expand a thread

[Antonio Leding]

Hello all,

Before filing a new FR, I wanted to ask if there is any way to 
auto-expand a given message thread?  I know this is somewhat possible 
using the “Thread Arcs” view and then clicking on what appears to be 
the lowest message in the arc but being able to either context-click or 
better yet, having a toolbar button would make this really simple…