Atto mixed vertical and horizontal alignment into a single selection,
which does not make any sense. It also used CSS classes in such a way
that those styles will break if/when Atto is removed.
This commit:
* removes the horizontal alignment from the dropdown - these are easily
achieved using the existing Tiny UI
* addresses a bug where existing styles (like horizontal alignment) were
not preserved when editing the image
* fixes a bug where the CSS selector was used instead of a CSS class
name
* recognises legacy TinyMCE class names and replaces these
* switches from using random class names to using Bootstrap class
utility classes for vertical alignment.
a68d9d5410