All schemas: Consider making horizons and odyssey flags mandatory

[Athanasius]

1. Historically the horizons and odyssey flags have been optional. In part this was probably due to CAPI being used as the source for some data.
2. Sending a null value has never been allowed for these flags. Sending false when it is not present might have been misleading in the future if the LoadGame semantics changed, as they probably will when the 4.0 Horizons client is available. They defined as having a boolean value only.
3. For Journal-sourced data we can easily make these flags mandatory (with a grace period for Senders to update). But there are several schemas (commodity/3, outfitting/2 and shipyard/2) that very commonly use CAPI-sourced data.
4. It is definitely possible to synthesize a horizons flag from CAPI data (EDMC does this). We would need to review current CAPI output to be sure if there is a method for synthesizing the odyssey flag.

Outside of schemas that could have CAPI data as their source we should give a notice period for making the flags mandatory, and them make them so.

For the (possibly) CAPI-sourced data we need to review the options.