feat(accordion): update examples and html structure.

[christiemolloy]

Related to this issue in Core: patternfly/patternfly#1913

In Core we added a new example and updated an old example of the Accordion, so that now there is one example that uses just <div> and <h1 - h6> in its html markup, and another that uses "definition list" <dl>, <dt> and <dd> in its html markup.

In Core we don't have defaults the same way that React does, but its important to keep the example order the same from Core to React. @jgiardino suggested that the default in React may be the definition list, and then if a user specifies a heading level it will use divs and h1-h6. patternfly/patternfly#1990 (comment)

[rachael-phillips]

@boaz0 will #2422 solve this issue?

[boaz0]

@rachael-phillips yes it will.