added a test for tagging/untagging. prepare to move most of tag/untag process to StreamTask class, not Stream.
Merge branch 'master' of https://github.com/cs2103aug2014-f10-1j/main
tidied up tag/untag process
some error in staging lines
improved and integrated the rank implementation
moved the SLAP-ped tag/untag methods to where they now belong
author-tagged most things
updated the tests to incorporate rank