Save import: extend the file format

[SapiensAnatis]

The current save import system essentially allows importing of a dump of /load/index. Unfortunately, this does not include all information relevant to the game state. It is notably missing Kaleidoscape data, endeavour lists, and event compendium progress - this data is loaded as and when needed by the game rather than at /load/index.

Dawnshard takes the opinionated approach that on savefile import, as much data as possible should be cleared and a blank slate created for the imported save. This has the side-effects, for example clearing endeavour progression. It's difficult to decide what to do here. Some players want to import a totally different save, such as a blank one to start over. Keeping endeavour progress in this case would be bad. Others want to make small tweaks to their existing save and re-import it, and are surprised to lose all of their endeavour progress.

The only way to achieve the desired behaviour in all cases, most likely, is to extend the data we export and accept from savefile imports, to include things like endeavour lists, Kaleidoscape data, etc.

This should be done in a backwards-compatible way, so that saves can still be exported and imported into Orchis.