Proper error handling and reporting

[singhpratyush]

Currently any server error returns an 500 with message Some error occurred. Proper error handling and reporting needs to take place. Different child classes of Exception can be kept in core/utils.py which will be used to track different problems as they occur.

def something():
    ...
    try:
        try:
            do_complex_operation_1()
        except MyException1:
            raise MyException2()
        ...
        try:
            do_complex_operation_2()
        except MyException3:
            raise MyException4()
        ...
    except MyException2:
        user_message = 'Error in operation 1'
        ...
    except MyException4:
        user_message = 'Error in operation 2'
        ...
    ...
    return_dictionary{'userMessage'} = user_message

This can be used at different levels to precisely track the error.