Fixed bug in the parser for finding the tags in a diary day.
Added code in the writeData function to upload the found tags to the
database and populate the entrytag junction table.
Cleaned up some querying in the writeData member function.
Implemented MainWindow::changeDay by calling the Diary::readDay.
Implemented Diary::readDay and made some changes to writeData to enforce
non-duplicate journal entries when resaving the same day.