Problem is that the main application actually does not create a pty and
instead uses the current one (for better compatability for ssh based
hosting).
The current problem is the fact that the child process should not
take over (and never give back too) the input / output handling of the
current pts. Such that both applications can receive inputs accordingly
(in best case actually controlled by the main application).
Renamed `Container.contents` to `Container.content` to be in line with
the corresponding `Element` function name. This has also been done for
the properties structs used by the `Container`.
This also means that currently the dynamic resizing through the app's
detached thread is not working, as it cannot send size updates. The
examples have been overhauled to still implement intermediate mode
applications accordingly.
The namespace shall also be used for testing the rendering of
`Container`s and `Element`s (including the `Scrollable` element).
The testing renderer currently is a striped down version of the double
buffered render without the secondary buffer and the flushing to stdout.
The internal `Cell` slice (the *screen*) is used for equality checks.
The testing namespace shall provide a way to describe the expected
`Cell` slices that should be validated against.
