Exception Overhaul

[AmericanEnglish]

The program currently has no exception handling whatsoever. The idea would be to do a complete overhaul of the source code to fix this. Exceptions, exceptions and error handling as far as the eye can see. Some minor examples:

1. Reading and writing to files which are already open in another program like excel.
2. Handling files which are not formatted correctly -> opening a CSV which was tampered with or malformed from crashing.
3. Other forms of IO error which might occur.