Some small changes

- Ask for a number again, if the user didn't input an integer
- Made addToList public and renamed it to isPrime, and renamed it's  parameter current to n. All of this is to make your program usable as a library
- Moved javadoc at the beginning of the class(it doesn't do anything at the end! If it's at the begining, when someone types in eclipse Main. It will show the javadoc)
- Added javadoc for isPrime()

Please check files changed to see all the changes