Strip most tags from abstract, hide unnecessary toolbar items

[greatislander]

Is your feature request related to a problem? Please describe.

The abstract (resource content) field allows all HTML tags supported by the WordPress classic editor. This causes weird formatting in some circumstances.

Describe the solution you'd like

We should filter the allowed tags, restricting them to:

• <p>
• <em>
• <strong>
• <a> (with href and rel attributes)
• <blockquote>
• <cite>
• <ul>, <ol>, and <li>

We should also modify the toolbar to remove all buttons for markup that we don't want added.

Describe alternatives you've considered

Not applicable.

Additional context

Not applicable.