Mongoose fixes per version and Added functionalities(priority tag with sorting and checkbox) and styling

[slyncrafty]

Fix

• Updated Mongoose queries to async/await per Mongoose 6+ compatibility.
• mongoose.connect()
• User.findOne()

Added functionalities

• Added priority tag toggle.
• Group priority Todo items before the regular todo items.
• Changed the way to mark completed item from clicking the task to checkbox.
• Applied centered styling/todo UI

Optimization

• Add ability to manually sort
• Add Due date and sort by due dates
• Add ability to organize by group/category
• Add functionality to alert via email