Add test case for catching ARI-3934: handleReplay throws BetterRequestException instead of ResourceNotAvailableExcpetion when the original for revisit is not found.
(test fails)
CLEANUP: around closest computation, redirect and Memento headers. 
re-formatting, removing trailing spaces, adding comments, dropping exceptions not thrown. no material code changes.
BUGFIX: stop throwing BetterRequestException from ReplayDispatcher.getClosest(), which can cause redirect loop if revisited original is missing in the index.
check if retrieved capture is in fact a revisited original before returning it from AccessPoint.retrievePayloadForIdenticalContentRevisit()
ref: ARI-3934.
(old code remains as comment. work-in-progress).
CLEANUP: WaybackException classes. code format and javadoc changes only.
Update Memento-related tests in AccessPointTest based on better understanding of Memento Spec and WB implementation.
Reorganize code for writing Memento headers.
Introduce BetterReplayRequestException for redirecting replay requests specifically. Avoid repeated response header updates in multiple places.
CLEANUP reformat code, add javadoc. no other code changes.
Implement soft-block feature.
  refactor handleReplay() with new ReplayCaptureSelector.
  add two tests for soft-block to AccessPointTest.
  other cleanups in AccessPointTest.
  CaptureSearchResults: add a method for checking robots flags with char
clean up and document CDXWriter classes.
Add revisit resolution test to EmbeddedCDXServerIndex.
clean up Oracle Exclusion classes.
Re-implement soft-block at EmbeddedCDXServerIndex
  (for capture search only, checking-in for testing)
FIX change to robotsflag by exclusion filter is wiped out before seen.
  add a test for this to EmbeddedCDXServerIndexTest
  refactor CustomPolicyOracleFilter in anticipation of making it Spring-configurable.
  add tests for CustomPolicyOracleFilter.
CLEANUP: fix indentation, remove trailing spaces, delete old code left as comment.
Add AccessPoint test of internal behavior important from performance perspective.
Hide the fact that the capture is a revisit, if the original is blocked.
clean up indentation.
make test exception text easier to identify.
Merge branch 'ARI-3879'

Conflicts:
	wayback-core/src/main/java/org/archive/wayback/replay/SelectorReplayDispatcher.java