Complete campaign loader
Remove legacy XML stuff from campaign loading
Remove legacy XML stuff from campaign saving.

Note that a campaign editor is not included in SMC; the Save_To_File()
(former Save()) function is currently useless. But hey, at least
we have one!
Remove more legacy XML stuff from level
Remove more legacy XML stuff from overworlds
Remove legacy XML stuff from level backgrounds
Remove legacy XML stuff from enemies
Remove legacy XML stuff from most general objects

This commit does not build!
XML loading for moving sprites.

This still doesn’t build.
Remove legacy XML stuff from enemy stoppers.

Still doesn’t build.
Typo