Stop storing tmux_pane

It can be retrieved with ps ewww -p, if necessary.
Track starts by temp file
Activation API

UI TBD.
Function to retrieve PID

This is surprisingly difficult to do while avoiding race conditions.
Don't open quickfix after synchronous dispatch

If another plugin has wrapped :Make in a construct that changes and
restores the current directory, opening the quickfix after a synchronous
make means restoring the directory for the wrong window.  Running
synchronously is already a vastly different experience than the other
adapters, so I think an additional small inconsistency is acceptable
price to pay for rectifying this behavior.