Add button to import and export list

[fappaz]

• Add buttons on the profile menu (for now)
• When the Export list button is pressed, a json file should be generated containing an array of items
• When the Import list button is pressed, it should open the file explorer. When a file is selected, it should try to import it as an array of items.
• Each item in the array should have name and status
• Limit to 255 items on the frontend

[fappaz]

I've decided to limit export/import lists to 255 items, which is only happening on the front end by now. In case this apps integrates with an API in the future, this business logic will be moved to the back end.