Add additional fields to save metadata

Implements feature #7618 (closed).

Summary of changes:

1. Add new fields to ESM::SavedGame to store current day and player's current and maximum health.
2. If these fields are filled (only in new saves), display this data in the save loading menu as two new lines.
3. Increase a savegame format. Older OpenMW versions can not load new saves, but they see them.

Notes:

1. Initially I wanted to use a date format from wait dialog instead of adding a new line for current day, but there is no free space with the larger font size for that.
2. ESS importer does not fill these fields, they are zeroes.
3. It should be possible to add empty lines to split data to blocks, but it will require to increase savegame menu height.