@nicolaszein: There is a limited import facility that you can access from the UI. Go to Banks and Cash Accounts/Import bank statement. This works well with CAMT.053 downloads from the bank, be it only for payments and receipts. But I gather from your question that you don’t have such downloads.
There is also an api, but it is not very well documented and you will need to find out a lot for yourself. Point your browser at http://localhost:55667/api2, assuming you have the desktop version with default installation. This will give you an overview of the available endpoints. Some more information can be found at https://manager.readme.io/. But again, you will have to find out much for yourself. Apart from coding, you will have to find a web host for your extension, or you will have to host it yourself.
Also, have a look at the Developer Toolkit at Two Free Extensions for the Community. It might give you a start.
Hope this helps.