Add broken debugging console.
Add instance for :debug-console command.
console: Set focus on line edit.
debug-console: Handle I/O and exceptions.
cmdhistory: Make history public.
Refactor different LineEdit classes.
console: Print prompts.
console: Set nicer font
Use a validator function for ConsoleLineEdit.

The prompts provided (e.g. sys.ps1/sys.ps2) could change during the lifetime of
the validator.
Stop history browsing at the correct places.
console: Never give focus to output view.
console: Add qApp to locals.
Make CommandPrompt aware of its prompt.
widgets.misc: Prevent moving cursor to prompt in CommandLineEdit.