Search2

[qinyeli]

Added searching

• Created searchRequest to filter selected data from the disk
• Created searchController and set the tableViewController as searchResultsUpdater
  • Implemented UISearchResultsUpdating method func updateSearchResults
• Set the tableViewController as searchBar.delegate
  • Implemented func searchBarCancelButtonClicked
• Brutally fixed the searchBar related UI bug by tableView.contentInset = UIEdgeInsets.zero in searchBarCancelButtonClicked and self.automaticallyAdjustsScrollViewInsets = false in viewDidLoad

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• Tagging function is not complete. Only the following functions are written (Ignore them in merging)
  • extractMessageTag() (a function that returns a list of tags given a string)
  • fetchMessageTag() (a function that returns a mapping from tags to tagCount