Test created for within period check

Refactored viewWithin period, fix, datePair != null, it can never be
null. //redundant code.
Add displaying id in viewAll and viewPeriod
Refactored date related test to DatePairTest

First commit
Merge branch
Merge remote-tracking branch 'origin/master' into search_logic

Conflicts:
	src/Logic.java
	src/Parser.java
	src/Task.java
	test/DatePairTest.java
	test/LogicTest.java
Merge remote-tracking branch 'origin/master' into search_logic
Update README.md

To include `completed` parameter for view. Now by default view command, only incomplete task will be shown. If user specify `completed` in `view`, then completed tasks will be shown.
Separated view for completed and uncompleted task
Merge remote-tracking branch 'origin/search_logic'
Merge branch 'master' of https://github.com/cs2103aug2014-w11-4j/main