WIP ignore tabs in windows

[mogenson]

A window with no tabs will have a tabCount of 0. A new tab for an existing window will have a tabCount equal to the total number of tabs (eg. 2 for the first new tab). The tabCount for existing tabs will be set back to 0. This means we need to capture and track each new tab when it is created. We cannot identify a tab later.

Create a getFocusedWindow() helper function.