Added accessors to check for hasNote, hasLocation, hasNoDeadline.

Changed some of the messages to display only the ones that have edited values, i.e. not the default unspecified version of it.
NOT WORKING YET.
Added if-statements to make necessary checks before dismantling the task into its subcommands.
Made edit build a new task so that a new object can be manipulated accordingly instead.
Edited ExactMatchSearcher's isTaskDuplicate checks to be more accurate.
Updated Undo's lines to fit the new singleton version of dismantleTask()
Merge branch 'master' of https://github.com/cs2103aug2014-t7-2/main

# By Yui Wei
# Via Yui Wei
* 'master' of https://github.com/cs2103aug2014-t7-2/main:
  fixed typecast for the comparator and made some methods private in edit.