Remove features that produce invalid html

[chasenlehara]

As a user of assistive technology (AT), I do not want the preview document to include obselete markup, so that my AT can accurately interpret and parse content.

The following markup can be included in the preview page and is obsolete:

• [ ] charset attribute on the a element
• [ ] name attribute on the a element
• [x] border attribute on the table element
• [x] cellpadding attribute on the table element
• [ ] summary attribute on the table element
• [x] big element
• [x] tt element

Ideally, these would not be a part of the WYSIWYG interface, although at a minimum, it would be good to advise authors not to use the features of the editor that allows these attributes and elements.

[chasenlehara]

@JessicaFrank I was able to remove some but not all of these options in the rich text editor. Similar to https://github.com/CCALI/a2jauthor/issues/232, I think we can provide guidance to authors that they should not use these attributes in the rich text editor.