add route 'prediction'; getSession within handle method
Merge branch 'huan' of https://github.com/owwlo/web_search_engine_course

Conflicts:
	src/edu/nyu/cs/cs2580/IndexerInvertedOccurrence.java
fix
Merge branch 'huan' of https://github.com/owwlo/web_search_engine_course

Conflicts:
	src/edu/nyu/cs/cs2580/IndexerInvertedOccurrence.java
session handler
session
show query recommendation on result page; result page animation
Merge branch 'huiyang' of https://github.com/owwlo/web_search_engine_course
add session history
update