fixed unit-v, questions_m and answers_m

-new answers.sql created for new column user_id
-new questions.sql created for new column user_id
-updated unit-v on required login to ask / reply questions
-updated question_m since user_name replaced by user_id
-updated answers_m since user_name replaced by user_id
schema changes on answers.sql and questions.sql

-changed user_id from int(3) to bigint(20)
get_answer_with_unit_id fixed in answers_m

-unit-v display for answers changed due to the change of
get_answer_with_unit_id function
before merge
Merge pull request #9 from m-mmoocs/Ask-question-fixes

fixed unit-v, questions_m and answers_m