docs: Corrected GET_ACCOUNTS comment--permission is 'dangerous'

Edit XML comments to note that GET_ACCOUNTS permission is 'dangerous',
not 'normal'. Made a couple of other Javadoc fixes while I had the
file open (summary sentences that were badly formatted, messing up the
Javadoc summary tables). NO CHANGES outside of XML comments.

See first comment for doc stage location.

bug: 25630412
Change-Id: Ic5f80b9f99e283dcf2f1cb9d2ab4a38138ec66e6