SE-342 LX-76 Make Blockstore work with MySQL

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   1. Description

Setup the devstack to use MySQL instead of SQLite. It defines new dependencies in requirements.txt file, deletes the old migrations and creates new one, modifies the Dockerfile to install the required alpine package and uses the MySQL service running as part of the edx devstack.

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   1. Testing Checklist

• [ ] All unit tests pass

• [ ] Check that Database migrations are backwards-compatible

• [ ] Manually test right-to-left languages and i18n
  of the changes.

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   1. Reviewers
      If you've been tagged for review, please check your corresponding box once you've given the :+1:.

• [ ] @symbolist

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      1. Areas to Consider

• [ ] Database migrations

• Are they backwards compatible?

• When they run on production, how long will they take? Will they lock the table?