CREImporter: Reorder file structure

A CRE file contains many structures describing the creature such as
memorized spells, inventory items, etc.

When the original engine produces a CRE file (for example as part of
a save file), it uses the following order:

Spells -> Item Slots -> Inventory -> Effects.

GemRB uses the following order which is slightly different:

Spells -> Effects -> Item Slots -> Inventory.

The CRE header lists the offset where a certain structure can be found
in the file, so a well coded program can read the creature information
regardless of the structure ordering. Indeed both the original engine
and GemRB can load the different save files correctly.

However, some programs (for example Shadow Keeper) cannot load
save files produced by GemRB due to this different ordering
in the CRE files.

This commit modifies the GetStoredFileSize, PutInventory, PutActor
functions so that CRE files are produced using the original order.
mailmap: merge Georgios' contributions