set default display list to be main task list, the user can choose to display main task list or done task list by indicating "done"
Merge branch 'master' of https://github.com/cs2103aug2014-w09-2j/main
change HISTORY_TASK_LIST to DONE_TASK_LIST
Merge branch 'master' of https://github.com/cs2103aug2014-w09-2j/main

Conflicts:
	JOYTZ/src/Analyzer.java