Make disk image build more reliable

ImageORL: Allocate buffer on stack instead of on heap and reduce buffer
size to 48K (allocating 64K on the heap is some kind of lottery)

Batch: Do not delete files while enumerating them, this sometimes skips a
file or two.

OberonFromScratch: Split the compilations and image building to even more
passes.

Now I can build the image several times in a row without intermediate
allocation failures - using the original memory layout.
Update documentation for Java emulator

Also, the feature LARGE_ADDRESS_SPACE is available for C and not Native
(yet), and the feature LARGE_PCLINK was not verified properly.
Simplify Javascript emulator sample page