Use symbols instead of strings in order clause

This simply changes the strings in the order clauses in the model. The
reason of the change is because the SQL generated when using symbols
automatically name spaces the column with the table name.

Topic.order(:title).to_sql
=> SELECT "topics".* FROM "topics" ORDER BY "topics"."title" ASC

This also changes the scopes using lamba to use stabby lambas for
consistency with other scopes.