resolve priority level problem
Fix bug in task test
add in task storage test
changes in task to string and string to task method
add test update
Merge branch 'chuyu-storage' of github.com:cs2103aug2014-w13-4j/main into pn-chuyu-logic-storage-merge
check null for updating tags
Merge branch 'chuyu-storage' of github.com:cs2103aug2014-w13-4j/main into pn-chuyu-logic-storage-merge
extract task converter class
clear the file before testing
modify for calendar parsing
Modified DateParser to convert string to calendar object, and wrote a test for it
Merge branch 'chuyu-storage' of github.com:cs2103aug2014-w13-4j/main into pn-chuyu-logic-storage-merge
Allowed adding of date in logic