Zangu a journey to space

Invalid date

New function:
1. Add a Data line chart for Classroom
2. SeaSymphony Level: Displays picture of new vocabulary within lyrics while playing a song

Updated:
1. Able to check your wrong answers at assessment page
2. Refined countermeasures for error handling of network

Fixed BUG:
1. Fix the bug where opening task list lead to error when installing for the first time and proceeded without completing update.
2. Fixed bug where the start icon does not display sometimes during user guide.