[8] Implement Product Design for Add Transactions

[JStonham]

1. Check whether command is budjen add.
2. Does the command pass validation? i.e. Does it include type, description and amount? Are they in the correct order e.g. amount immediately before number? Will need a separate class for this.
3. Take string array into transaction object.
4. Add to transaction date.
5. Manual testing for missing code (bugs) using travis.

[kinbiko]

So the main new components are:

• [x] a Validator for checking that the input coming from the user made sense
• [x] a Converter for turning this input from the user into a Transaction object.
• [x] Then we need to add this new transaction to our existing data