Add comment in cellForRowAtIndexPath: why do we always use self.tableview to instantiate a table view cell
add comment in sectionIndexTitlesForTableView
update search result table view for search string
add dealloc method for debug
1. Make the border of status bar invisible
2. extract data source related method from viewDidLoad to private method
add function: push a view controller when table view of DictionaryViewController is clicked