Fixed docblock and indents

Signed-off-by: Shivam Dixit <shivamd001@gmail.com>
Added comments in contest details model

Signed-off-by: Shivam Dixit <shivamd001@gmail.com>
Added contest challenges model

Signed-off-by: Shivam Dixit <shivamd001@gmail.com>
Added contest submissions model

Signed-off-by: Shivam Dixit <shivamd001@gmail.com>