Add append function for conditional dates
Removed isConditional field in task
Merge branch 'pn-modify-conditional-task' of github.com:cs2103aug2014-w13-4j/main into pn-modify-chuyu-storage

Conflicts:
	src/models/Task.java
removed is_confirmed enum
Merge branch 'pn-modify-chuyu-storage' of https://github.com/cs2103aug2014-w13-4j/main into chuyu-storage
get all tasks get all tasks that are not deleted