Get and safe AmEx transactions

[dgor82]

• [ ] Find out if there is a way to access via API (see Monzo's ability to show AmEx transactions - but is it public?)
• [ ] If not, either look for a library that can read ofx file
• [ ] If not, implement an importer for AmEx's Excel or CSV format.
• [ ] Save raw files locally
• [ ] Represent in memory in common bank transaction format