List pre-requisite

[davidlang42]

Handle brackets to specify the required LIST of the task which is a pre-requisite (rather than always meaning DONE):

• list status exact: {TASK(LIST)}
• exact or to the right: {TASK(>LIST)}
• exact or to the left: {TASK(<LIST)}
• default means DONE: {TASK}

Make sure that direct updating from TaskBan edits still works (see #27)