Migrate tcell to 2.0.0
* tview.TreeView#SetSelectedStyle removed
* tview.Primitives don't allow directly setting attributes for now (might change again with tview 2.+)
* Directional focus changing doesn't happen in tivew anymore, instead
the application can handle it itself. This gives the application more
power over the focus and the user input handling.
* Key events now trickle down from parents to children, this allows for
defining a set of events for a whole view without having to set it in
the tview.Application instance or having to register multiple handlers
for one event.
Marcel Schramm