Refs #4476, #4494: Simplecache refactors for better AMD + static view file support

Main changes:
 * Url is now: /cache/:timestamp/:viewtype/:view (Note: no file extension unless part of view name)
 * When simplecache is off, use /ajax/view/:view?view=:viewtype
 * Better mime type guessing for /ajax/view

Demo: http://elgg19.ewinslow.com