Added search 'past' and search 'future' functions.
Merge branch 'master' of https://github.com/cs2103aug2014-T13-2J/main

# By mervynwee (2) and Nee Si Yao (1)
# Via mervynwee
* 'master' of https://github.com/cs2103aug2014-T13-2J/main:
  Fix bug where undeleted tasks are added to deletedTasks file.
  Allow the program to store a persistent list of deleted tasks so that the program can use it to synchronize the deletion on google calendar if the user did not have internet connection at the time of deletion. Works with undo feature. Create a new test function in StorageTest to test updateTaskHistories and revertTaskHistories.
  Rename hasChanges to hasBeenUpdated. Edit error message in DeleteHandler to be more user-friendly.