Added methods isContainedInList, getTaskContainedInList, updateTaskTagsHash; Modified markTaskDone method in TaskList; Modified Undo/Redo in TaskList (modified other corresponding methods to fit)
Added methods isContainedInList, getTaskContainedInList, updateTaskTagsHash;
Modified markTaskDone method in TaskList;
Modified Undo/Redo in TaskList (modified other corresponding methods to fit)

CS2103TAug2014-W15-4J/main