Exposing access to the working directory to QML is the first step towards enabling usage analogously to a normal terminal emulator alongside the management of multiple running appications.
i.e. executing `cd` should change the global working directory so that consecutive commands work as expected.

Previously `kill` merely destroyed the terminal widget. This is contrary to the expected notion of `kill`, i.e. actually killing the process explicitly instead of relying on side effects.

The normal mode `d` verb now explicitly destroys the current item's content, be it a terminal widget or a history view.

i.e. serialize objects to JSON.

Trailing whitespace was falsely recognized as a separate argument and as such led to resetting configuration values without obvious cause.

This enables the user to straight forwardly change all application settings via command mode.

During the implementation of this change I discovered that the way I was passing around `StateHandler` and `SettingsHandler` instances using properties was unnecessary. If all object instances are created in a common hierarchy they can access each other by their `id` property - i.e. `settings` and `mode` are available to the whole application without property trickery.

Otherwise they are not accessible to JS commands, i.e. they can not be changed in command mode.

`list` holds the components of the central list UI element.
`command` holds the UI and implementation parts of the command mode.
`widget` holds more or less general purpose elements that may also be of use in other circumstances.