added 'add' function

pending storage query method
added some constants for use in logic

added for add and deletion
added delete function for tasks

deleting specific tasks done, pending query for tasks and deleting
method for storage.
added message for deleting task
added exception throwing

-add and delete throw when they are unable to add or delete from storage
modified throwing

-changed from throwing error to throwing exception
added message for editing task
added edit method

- edit takes in 2 Task objects
- first is the task to be edited which is deleted
- second is the edited task which is added
modified delete method

- removed deleting after listing method, leaving it for later in project
if possible
removed some constants

- removed constants for adding and deleting task
changed methods to void

- add, delete and edit methods changed to void
- modified code to throw exceptions if unable to add, delete or edit
modified edit method

- added try and catch blocks to handle exceptions
Revert "modified edit method"

This reverts commit a28cb8fe2126549a3c58ceda7232880ad3351814.
Revert "changed methods to void"

This reverts commit 3539c12a3afec3d60eba272028ef939d42d1ec75.
Revert "removed some constants"

This reverts commit 71282695077b41bbb58713fcf6bb22e0d4050917.
modified edit method

- removed instance of Logic
- did not know you could access directly the add and delete
Create Gui.java

Basis GUI.
Update UserInterface.java

updated UI template.
Update UserInterface.java

1st versions of add(), list(), delete(), edit(). Just display feedback, no info.
modified edit

- changed edit so that it will terminate if either delete or add fail
- it will also throw different exceptions depending on which exception
was thrown from add or delete
- else it will throw a default exception