Warn when BIDSVersion exceeds latest version at time of release

[effigies]

trafficstars

If a dataset declares itself to have BIDSVersion of 1.9.0, it likely is doing so because there are things specified in 1.9.0 that were not present in 1.7.0 or 1.8.0. Or, perhaps, they might have made a mistake (such as using the validator version instead of the spec version).

It probably makes sense for the validator to have a concept of what versions it knows about and can at least warn that the user might need to upgrade to properly validate their dataset.