ACCUMULO-2745 Update README files with license headers

  Replaced readme.txt without a license header with a README that has one, for
  naming consistency.
ACCUMULO-2750 Remove unused state diagrams from docs module

  These files would be better suited on the website or in a wiki.
ACCUMULO-2751 Remove outdated ScaleTest.odp presentation

  This file would be better suited on the website somewhere, if kept at all.