WIP adapt DW PR#2568 to use accumulo PR#4898

[keith-turner]

These draft changes build on #2568 with the following differences.

 * Compute bulkv2 load plans using new unreleased APIs in accumulo PR
   4898
 * The table splits are loaded at the beginning of writing to rfiles
   instead of at the end.  Not sure about the overall implications on
   on memory use in reducers of this change.  The load plan could
   be computed after the rfile is closed using a new API in 4898 if
   defering the loading of tablet splits is desired.
 * Switches to using accumulo public APIs for writing rfiles instaead of
   internal accumulo methods. Well public once they are actually
   released.
 * The algorithm to compute the load plan does less work per key/value.
   Should be rougly constant time vs log(N).
 * Adds a simple SortedList class.  This reason this was added is that
   this code does binary searches on list, however it was not certain
   those list were actually sorted.  If the list was not sorted it would
   not cause exceptions in binary search but could lead to incorrect load
   plans and lost data. This new SortedList class ensures list are
   sorted and allows this assurance to travel around in the code.  Maybe
   this change should be its own PR.

These changes are not yet tested.