Partial cleanup of the point cache UI panel, using a number of booleans
to store all the stupifying special cases. Not complete and will need
a general overhaul anyway ...
Make the archive file name construction based on PointCache settings
internal to the path utility function.
Build the archive filename inside the base Reader/Writer constructor
from info in the PointCache. This way we can replace it more flexibly
with other data streams, packed files, memory buffers etc.