[MySQL] Custom collation for just one column in table

[trogwarz]

For issue #661 – add support collation for MySQL adapter. Now allowed this usage:

// ... Somewhere in migration ...
$this->table('foo')
    ->setOptions([
        'encoding'  => 'utf8',
        'collation' => 'utf8_general_ci',
    ])
    ->addColumn('text_one', 'string')
    ->addColumn('text_two', 'string', ['collation' => 'utf8mb4_unicode_ci''])
    ->save()
;

[trogwarz]

TODO: check if this is available for other adapters (i don't have enough experience with other databases).

[trogwarz]

Just can't run these tests on my environment. Please, check them and fix is there are some issues with this test.

[shadowhand]

Thank you for contributing! The branch you made this PR against is no longer accepting patches. This probably happened because we didn't merge your changes fast enough. 😭

Please create a new PR against the current default branch if you want to see these changes merged.