Refined Task unit tests

> Better tests for equals function
Added code to allow marking Task obj as block type

> Updated some comments
Added unit tests for isLaterThan function
Improved switch cases in DatabaseLogic

> Added assertions
> Improved code
> Fixed bug with permanent deletion of already deleted Task obj
Resolves #182, refactored DatabaseFacade
Cleaned up code

> Added assertion in DatabaseLogic
> Reworked try blocks in DatabaseLogic and TaskReader
> Removed unnecessary code in Task
Added and updated unit tests

> Added unit tests for DatabaseLogic
> Minor fix in TaskTest
#182, more refactoring

> Cleaned up redundant code
Added unit tests for TaskReader and TaskWriter
Merge branch 'master' of https://github.com/cs2103aug2014-t15-1j/main