Support KDBX 4.0 database format

[phiresky]

Since upgrading my database to KDBX 4.0 I'm getting this error:

KpioDatabaseError: Invalid header field ID. The database might be corrupt.
    at Instance.parseDatabaseHeader (.../node_modules/keepass.io/lib/KeePass/KeePassDatabase.js:82:23)
    at .../node_modules/mout/function/bind.js:13:23
    at fn (.../node_modules/async/lib/async.js:752:34)
    at .../node_modules/async/lib/async.js:1252:16
    at .../node_modules/async/lib/async.js:697:43
    at Immediate.<anonymous> (.../node_modules/async/lib/async.js:1245:34)
    at processImmediate (internal/timers.js:456:21) {
  name: 'KpioDatabaseError',
  message: 'Invalid header field ID. The database might be corrupt.'
}

New databases are created in this format by default.