Implement Accounts.
Rename bank_id to acct_id.

- acct_id more accurately reflects the uniq account id given by the bank.
- "_id" or "id" are not acceptable field names.
Implement Balance and Transaction.
Remove AccountBalance and svg diagrams.
Edit gitignore.
Merge pull request #1 from jcdavison/restructure-institutions-accounts

Restructure institutions accounts