Improvements to "Templates" section

[kilfoyle]

@eedugon had some very nice suggestions for the Templates section.

Notes:

• We need separate sections for index templates and component templates, with anchors for each.
• The Create or update component template API content is nice, and should be incorporated into the page.
• The Manage index templates page was duplicated in the former Manage indices in Kibana page, which is now incorporated into Index basics. The former should be removed and we can link to the latter.
• Maybe we can organize the text a bit better, with bullets, etc.