Make Piece to show its length on edit prompt

Signed-off-by: Juan Martin Runge <jmrunge@gmail.com>
Add alert function

Signed-off-by: Juan Martin Runge <jmrunge@gmail.com>
Validate length input format

Signed-off-by: Juan Martin Runge <jmrunge@gmail.com>
Update playlist duration

Signed-off-by: Juan Martin Runge <jmrunge@gmail.com>