Added gitignore rules to stop tracking class files

Added a .gitignore file so that git will no longer track changes to the automatically generated class files. It appears to be good practice to not track these changes since they change so frequently, and can just be reproduced automatically by compiling the tracked source code.

In order for the gitignore rules to take effect, the class files were removed. Since the bin directly has no files any more, it is removed as well. 

We might want to consider ignoring accounts.csv as well, unless we want all developers to be using the same, tracked portfolio data.