WIP/POC - Add database migrations capability using Phinx.

[noplanman]

Proof of concept to allow easy database migrations using Phinx.

Before anything like this gets merged into core, we really should think about a centralised config management, like using phpdotenv or just a simple config.php that contains all configurations and credentials.

Probably makes sense to merge the Manager into core!

@akalongman In the scheme of things, I look forward to see how the migrations could work with Laravels DB library, which would also allow the whole DB management to become muuuch cleaner and easier.

[akalongman]

@noplanman please take a look #963

[asafov]

I can help with write migration files for phinx.

[noplanman]

Thanks @asafov, this PR is a proof of concept and for sure the DB structure needs to be "clean" and nice before putting any more work into this 👍