Error Handling added

I fixed up some bugs with the program, and added some error handling.

So if an image hasn't been opened and you try to hit "next image" it will report back an error and tell the user that they must open up a directory. If the file that's being opened from the directory isn't an image it gives an error, if the user tries to perform an action and an image hasn't been opened it gives an error.

All the errors are covered in the help document as well.

There is now a button on the program that will open the help file up as well.

Code is on SVN