update core_symbol

- correcting spelling errors, and caps
- better bash commands
- simpler command line to launch the script
- improved prerequisites
- include steps to follow after prerequisites

1. args.contracts_dir doesn't end in a forward slash, therefor when it is concatenated with a subpath, the subpath has to start with a forward slash; this pattern is present in other similar variables as well
2. system contract has to be initialized before it can be used (e.g. creating staked acconts)
3. commands list updated to include the new addition stepInitSystemContract
4. readme.md updated as well to reflect the current status of the script and requirements

updated the exchange_tutorial script to use a new account name (tokenxchange) that will not conflict with any use of the exchange account that the user might have; and changed EOS to SYS

Added new adversary wasms, none of them pass dissasembly so more effort will need to be taken to see if the exploit can pass our basic validators and make it onto the chain

Changed paths to reflect recent refactoring from the programs directory to the tutorials directory.