Squashed commit of the following:

commit 0449cd63f7
Author: Nikita Zlobin <nick87720z@gmail.com>
Date:   Fri Oct 5 02:19:23 2018 +0500

    carla skin: fancy item selection

commit 84a7b527a7
Author: Nikita Zlobin <nick87720z@gmail.com>
Date:   Fri Oct 5 02:10:49 2018 +0500

    carla skin: drawOutline: fixed positioning and optimization

commit 30681d1523
Author: Nikita Zlobin <nick87720z@gmail.com>
Date:   Fri Oct 5 01:20:53 2018 +0500

    carla skin: drawOutline: set brush only once

commit 63d2ab2e21
Author: Nikita Zlobin <nick87720z@gmail.com>
Date:   Thu Oct 4 00:10:39 2018 +0500

    carla skin: more neat QColor to tuple conversion

commit 2137b78109
Author: Nikita Zlobin <nick87720z@gmail.com>
Date:   Wed Oct 3 16:35:48 2018 +0500

    rack item: Skin-independent colorization support

    Color menu item tints background color, preserving all visible
    relief. No need to lock it for some skins.

commit 13fa4f2c34
Author: Nikita Zlobin <nick87720z@gmail.com>
Date:   Wed Oct 10 15:00:58 2018 +0500

    rack list: Colorized padding

commit 9964af1994
Author: Nikita Zlobin <nick87720z@gmail.com>
Date:   Fri Sep 28 17:48:17 2018 +0500

    rack list: Colorized rails

commit d212577057
Author: Nikita Zlobin <nick87720z@gmail.com>
Date:   Wed Oct 10 14:12:36 2018 +0500

    rack list: Set frame in ui form

commit 9a7e060988
Author: Nikita Zlobin <nick87720z@gmail.com>
Date:   Fri Sep 28 18:44:49 2018 +0500

    rack list: Set common frame