#6 list item functionality

Completed:

1. ListItem basic class definition + functions Fields added

• 'static': nextItemId
• itemId
• startDate
• endDate
• priority
• itemTitle
• itemNotes
• isFlagged
• tags Fields are public scope with relevant setter functions. I also added some unit tests for the list item.

2. Setup Compose Library

• you can build and run Main.kt