no-icon when saving without custom icon fixed

When no custom icon was loaded for the container and the scene file is
saved, the container would not have any icon displayed at all. This was
fixed in `ContainerObject::Read()`

Minor typos in the code description have been fixed.

`ContainerObject::OnDescriptionCommand()` was cleaned up by introducing
a new function `ProcessLevel()` which hides/unhides a hierarchical
level as required for hiding/unhidung tags or objects.

The global functions `ChangeNBitRow()` and `CountNBits()` have been
turned into static functions.
Fixed potential crash trigger
Implemented container loading command
Added Password Protection, enhanced undos

By double clicking on the container icon in the object manager while
holding CTRL, the password protection can either be enabled or disabled.

Undo problems have been fixed: Loading/clearing the icon as well as
packing and unpacking the container now create new undo steps.
Removed GetDescID() macro

Since it was 1. invalid and 2. the corrected version would not really
bring benefits in terms of less writing work.
undo for protection, un/-packing when un/-protecting
Added link translation when loading a Null-Object
Fixed "Load Container", added "Prepare Container"
Replaced icon and updated README accordingly
Removed R15 compiled binaries
Added R13+ Windows Release builds
Removed binaries for now
Adjusted "Prepare Container" name
Fixed broken links

Links to the top-level object which is replaced by the two commands are
now retained.

Added Todo notice.
Fixed initial parameter-values of the Container
Updated TODO: Bug with undoing prepare command
Updated Makefile to newest version
Updated name of "load to container" command
PrepareContainer: Fixed bits and undo

Not all bits where copied from the original container before, which is
fixed now. Undoing the Prepare Container command did not work properly,
which was also fixed.
Fixed undo problem with PrepareContainer command