The functionality was largely duplicated across the commands, and with
regard to naming, `FocusRunnerPane` better maps to how I use it.
Closes#35 - Unify Focus & Zoom runner pane functions
Closes#5 - Accept arguments to OpenRunner command for context specific
runners
This allows for specific variants of the VtrOpenRunner command to be
mapped allowing for context dependant runner orientations, sizing, and
initial command.
In order to avoid rapid flickering of runner window as it is created
and initialized, create and initialize it in a temporary background
window then bring it in.
