Typos and text corrections

[mauromsl]

• Replace misstyped 'poofreading' with 'proofreading'
• Fix discord notification not being interpolated: [olh] {user} has {action} the proofreading assignment for {article} assigned to {proofreader}
• Fix wrong discord notification raised when requesting a proofreading assignment [olh] Typesetting task 18 cancelled by editor (Check that it is just a wording issue and not that the task is wrongly being cancelled)