Pkb affectsBip affectsBipStar APIs (#296)

* derive and implement affectsBip API

* update uni tests

* separate derive affectsBip table to only upon query

* implement affectsBip* API

* comments for affectsBip/* and helper functions

* Merge branch 'master' of https://github.com/nus-cs3203/team20-win-spa-20s1 into pkb/affectsBip

# Conflicts:
#	Team20/Code20/source/PKB.cpp
#	Team20/Code20/source/Pkb.h
#	Team20/Code20/source/PkbQueryInterface.h

Author: choonx99