Better selectedText handling

New way to write selectedText (now a string) where %1 will be replaced with the number of items selected and %2 with the total amount of items.

Example (and default by the way) : "Selected %1 of %2"
Added plural "s" handling for selectedText

You cna also use %s1 and %s2 to display the letter "s" if number of selected items is > 1 or total number of items > 1 respectively.
Changed default text to easily see the change to : "Selected %1 item%s1 of %2 item%s2"
Merge pull request #14 from Lynesth/master

Better selectedText handling