filename shortening needs file extension to make decisions.
closes #PICARD-613
Merge pull request #344 from xlotlu/master

filename shortening needs file extension to make decisions.
Added a menu option to add new files to tagger

A file is considered 'new' if it has been modified in the last five
hours. This setting can be stored in the config later.

Only the starting directory is scanned for new files currently. A
context menu option can be added to the treeview to add new files from a
folder.
Load new files while adding a directory

The file menu option has been removed and has been replaced with a
combobox in the "Add Directory" dialog.

The combobox is uneditable for now and just contains some pre-defined
periods as there didn't seem an easy way to take input from user.

The dialog looks a bit odd with a button 'missing' -
http://i.imgur.com/QOmhzr2.jpg