[Feature] GUI for adding a new entry.

[ScottCTD]

Initiations

• Currently, we have the InsertEntryUseCase, but we don't have ways for users to insert (add) an entry.

Design

• After clicking the "Add Entry" button, we may want to open a dialog for users to fill in the information of the newly added entry.
• After filling in the information and clicking the "Confirm" button, we may need to validate the information to make sure they are in the correct format.
• Then, the InsertEntryController is called.
• After all, the BillUpdateController should be called to update the screen to display the newly added entry.

Details

• If we are adding a splitter entry, then we need a way to inherit the information from the parent normal entry. This may be solved by implementing some enhancements in the use case layer.

TODOs

• [Feature] Design and implement a new dialog for adding an entry. #69
• [Feature] Connect the "Add Entry" dialog to the InsertEntry and BillUpdate use cases. #70
• [Feature] Use some datetime picker to edit the date. #79
• [Feature] Add support for adding a splitter entry. #80
• [Improvement] Create a separate class for the dialog of adding an entry. #81
• [Feature] Add a use case to fill in the inherited attributes of a splitter entry automatically.  #91