This PR split the `Board` into two parts. One is the struct has been
renamed to `Column` and the second we have a `Template Type`.
But to make it easier to review, this PR will not change the database
schemas, they are just renames. The database schema changes could be in
future PRs.
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Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: yp05327 <576951401@qq.com>
