Improve Task List Window Ui

Task list window ui is improved.

Display Version Number Correctly

Fixes the bug of displaying wrong version number in Gui.

Improve Ui response

1. Task Index Parsing Improvement
   In v1.0, if the input task index contains spaces, e.g. "1 ", Duke cannot parse it and will treat the input as invalid.
   In v1.1, Duke can parse such index now.

2. Untagging tasks with no tag
   In v1.0, untag is replied the same no matter if the task had any tag or not before untagging.
   In v1.1, if the task previously does not have tag, that will be told to the user after using untag.

Supports Gui

Duke uses Gui now.

Duke

Duke is a console program that can save tasks.

Use java -jar Duke.jar in console to run the program.

Commands supported:

1. list - show task list
2. todo - add a task with no time description
3. event /at - add a task with time description
4. deadline /by - add a task with a deadline
5. done - mark the task with the index as done
6. delete - remove the task with the index from the list
7. bye - turn off Duke program

Supported time formats:

1. yyyy-MM-dd hh:mm:ss
2. yyyy-MM-dd
3. hh:mm:ss
4. hh:mm
5. any description, but cannot be compared with other time

Tasks are automatically saved (at exit) and loaded (at start).