Use umzug as migrator engine

This PR replaces the migrator engine of sequelize with umzug. It is backwards compatible with the previous migration schema but enforces the new table structure. D

!!Do not merge this PR yet!!

To do:

- [x] Support for new migration file schema (disable promisification via config file)
- [x] Script for migrating the old table structure to the new one.

(as in - I see from the code where it will be stored, I just think that should be mentioned in the help text ;) )