subject mail populated when user shares file/folder

in response to @rperezb issue #767 , the subject mail is now populated when the user shares either a file or folder. I also kept the same syntax as it is on the web, with file/folder name surrounded with greater and less signs. 
I created an additional parameter, passing in the context of the application to CreateShareOperation, in order to get the strings from strings.xml. If I should do it another way, I can do so immediately.