initial shuffle of the API guide nav to add introduction

* revise to the Compatibility doc, put it in Intro
* put Permissions in Intro
* put App Fundamentals in Intro
* move Manifest docs to the top of side nav tree
* move App Resources above UI
Will perform another fix to the Best Practices section
later to deprecate some docs there and point to Training instead

Change-Id: I88a8f94167ba15e97eb3bbbc08fd82dd82498e4b