cherrypick from mnc-preview-docs docs: Preview 3 permissions docs.

Original Change-Id: I4eaf45d98846e2bf9456f5896da4ec3079f4ba18

Added section describing the new support library methods. Also
updating lists of normal and dangerous permissions based on current
AndroidManifest in mnc-dev, as well as any other changes brought to my
attention.

See first comment for doc stage location.

Change-Id: I4eaf45d98846e2bf9456f5896da4ec3079f4ba18