Merge the two default custom search templates and update them for 3.2 markup / accordion use

Previously we had 2 "default" search templates for custom searches.
templates/CRM/Contact/Form/Search/Custom.tpl - used by default when no templateFile() function was explicitly included in custom search class
templates/CRM/Contact/Form/Search/Custom/Sample.tpl - referenced explicitly by many custom searches

For this issue:

• Update Custom.tpl so current markup standards for accordions and form.
• Modify existing searches in repository to point directly to Custom.tpl. (This is technically unnecessary - but helps clarify that each search can define it's own template file.
• Modify Sample.tpl so it simply points to (includes) Custom.tpl (for backwards compatibility).

Going forward, developers can just omit the templateFile() function if they want to use the default search template. Or point explicitly to a custom custom search tpl file.