Renamed contextual/contextualtoolbar~ContextualToolbar to balloon/balloontoolbar~BalloonToolbar.

[jodator]

Suggested merge commit message (convention)

Aligned docs after ranaming ContextualToolbar to BallonToolbar.

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Other: Rename ContextualToolbar to BalloonToolbar. Closes #ckeditor/ckeditor5/550.

Additional information

Updated repositories that uses above mentioned toolbar are:

• https://github.com/ckeditor/ckeditor5-core/tree/t/ckeditor5/550
• https://github.com/ckeditor/ckeditor5-editor-balloon/tree/t/ckeditor5/550
• https://github.com/ckeditor/ckeditor5-image/tree/t/ckeditor5/550
• https://github.com/ckeditor/ckeditor5-ui/tree/t/ckeditor5/550

Proposed merge message for those branches:

Aligned code after ranaming ContextualToolbar to BallonToolbar.

but for: https://github.com/ckeditor/ckeditor5-ui/tree/t/ckeditor5/550:

Other: Rename `ContextualToolbar` to `BalloonToolbar`.  Closes ckeditor/ckeditor5#550.

BREAKING CHANGE: Renamed `contextual/contextualtoolbar~ContextualToolbar` to `balloon/balloontoolbar~BalloonToolbar`.
BREAKING CHANGE: Renamed `contextualToolbar` configuration option to `balloonToolbar`.