- remove 'after()' in adding id column for group_member table migration
  which is not working properly after rolling back and replay
- rename 'action' column to 'action_id' in acl table to be consistent with renaming
  of group and user columns to group_id and user_id respectively in
group_member table.

- add an id column to acl table as Laravel does not allow composite
  primary key
On MySQL, you do not need to drop the primary key, which is created with column creation.
You only have to drop the column, otherwise, MySQL will give error. I
have removed drop primary key lines from two migration files.