Handle data format version in loader and f/e

[mwinokan]

@tdudgeon please inform @kaliif where the data versioning will be in the XCA output for the loader to parse.

In the case where the major version differs between the new data and existing target then the upload should fail without trying

[kaliif]

@mwinokan @tdudgeon something occurs to me only now - how do I know what the current version is? Is there maybe an online resource I can check?

[mwinokan]

@tdudgeon says the data version of XCA is in the yaml output and this can be compared to the data version of previously uploaded targets.

@kaliif please bake in the supported data format major version in the loader code, i.e. currently it's version 2, and in future if there are breaking changes with XCA it will be version 3.

@boriskovar-m2ms points out that the f/e should show the data version in the target settings and flag targets with outdated data version as a toaster warning when opening the target.

@kaliif the above will require having the current version as part of the django context

@kaliif please also see about adding the current data format version to the version endpoint so that it can be shown in the hamburger menu

[mwinokan]

@kaliif will need incremental upload test data, and @mwinokan suggests taking the A71EV2A tarballs from the production stack.