add new method to print

-add toFileString() which immitates toString() but is in the format that
can be used to write to a file
remove method and update javadoc

-remove gatherFileContents() method as it is now replaced with to
gatherSMSFromFile() which uses createSMS() as a helper
- Added some javadoc
add save file dialog when merge selected

-when merging files, a save dialog will now pop up to let user select
file to save to
add @override annotation to toString()