Imports of dump_tree command

PathSynopsis
flagPackage flag implements command-line flag parsing.
fmtPackage fmt implements formatted I/O with functions analogous to C's printf and scanf.
github.com/golang/glogPackage glog implements logging analogous to the Google-internal C++ INFO/ERROR/V setup.
github.com/google/trillian/storage/tools/dump_tree/dumplib