Tool's tabs (sidebar) improvements

[ghost]

Make Tool's tabs ergonomy similar to LibreOffice 5.x Writer sidebar, with possibility quick show/hide opened tool tabs

• https://design.blog.documentfoundation.org/2016/02/26/what-do-you-expect-from-the-sidebar-in-libreoffice/
• https://www.youtube.com/watch?v=AdgKVJaCtpQ

[sk1project]

Good mockup. We will pay attention for it in future.

[ghost]

Also take a look on this

• https://blog.documentfoundation.org/blog/2016/12/21/the-document-foundation-announces-the-muffin-a-new-tasty-user-interface-concept-for-libreoffice/
• https://design.blog.documentfoundation.org/2016/12/21/evolving-past-the-restrictions-of-toolbars/