Delete line action, plus undo implemented for various commands

[machinewrapped]

• Added delete line command, with an undo option.
• Implemented undo stack.
• Added support for multiple viewmodel updates in a command.
• Fixed the viewmodel updates for several commands.
• Implemented undo for several commands.
• Use queued connections as much as possible to reduce deadlock danger

[machinewrapped]

• Added delete line command, with an undo option.
• Implemented undo stack.
• Added support for multiple viewmodel updates in a command.
• Fixed the viewmodel updates for several commands.
• Implemented undo for several commands.
• Use queued connections as much as possible to reduce deadlock danger
• Prevent renumbering of lines except when writing translated subs, so that reparse translation doesn't overwrite the wrong lines
• Unit tests for all commands that support undo