Drop support for saves made prior to 0.45
To quote @akortunov
I'd also suggest to drop a support for ancient savegame versions prior to 1.0 release. For ancient saves we can display an advice to re-save samegames via 0.x OpenMW version, which release version will understand. It will allow us to drop a lot of legacy code, and t will be much harder to do it after 1.0 release.
and @psi29a
At some point we'll need to drop a lot of these backwards compatibility things. Do we have a policy yet on this? I would at least have it that we are backwards compatible to the last major release. Anything before that isn't compatible. We'd request that they upgrade your save via releases to catch up to latest.
There is a desire to drop support for saves made in older versions. The amount of code that could be removed if we do is ever increasing. Removing version checks and unused members of the save specific ESM structs would also be a good opportunity to upgrade any parts of the ESS converter that still use them.
I propose we maintain a rolling model where we always support saves made by the previous two stable releases. This way 0.48 would only support 0.47 and 0.46 in addition to its own saves while 0.49 would only load old saves made in 0.48 and 0.47.
I'd also like to tell the user which version of OpenMW they should use to upgrade their save, which would mean maintaining a table mapping save game version ranges to OpenMW release numbers. For example, 0.49 would still be able to tell you to use 0.47 to convert a save made in 0.30 and perhaps it could also warn users that they might need to go through several OpenMW versions to fully convert their save.