Help Text for CKEditor's Font Style CSS classes needs improvement.

Problem/Motivation

The ability to add multiple classes to an individual element is not readily apparent in the current description text.

Proposed resolution

Add a line of text to the description text explaining this, which could probably do with some community review.
"Multiple classes may be added to an individual element.
Example: Small Title=h2.small.title"

Remaining tasks

• Communally agree that the text is either good or terrible.
• If it is terrible, adjust it.

User interface changes

Update to the description text in wysiwyg_ckeditor_settings_form().

API changes

None.