WYSIWYG: Improved a range of text direction/alignment scenarios

WYSIWYG: Improved a range of text direction/alignment scenarios

- Removes 'span' from being a valid part of alignment formats so it's
  not used to align contents, since it's going to mostly be an inline
  format, wheras you'd really want alignment on the parent block.
- Adds direction cleaning to all direction change events, to remove
  direction styles and child direction controls which may complicate
  matters and cause direction changes not to show.
- Makes text direction controls work with table cell range selections,
  which TinyMCE does not consider by default, via manual handling.

For #4843