rename JESConfig.txt to .properties in launchers

While I'm moving the location of the config file, I decided it would be
a good idea to change the format to a .properties file to make the file
less fragile and easier for users to understand.

This commit implements the changes in the launchers, which are really
just "change JESConfig.txt to JESConfig.properties." The code itself
still stores it in JESConfig.txt in the home directory, but the next
commit will implement the new configuration handling.
remove legacy Python configuration code

And now I know why a one-unlabeled-value-per-line format is used...
because the configuration code used to be spread out all across the
codebase. This commit removes any commented-out code that, from my
inital inspection, was used to read the legacy config file format.
store settings in .properties file

This new configuration format is much more future-proof and resistant
to accidental changes. The new JESConfig class is interface-compatible
with the old, so there shouldn't be any incompatibilities resulting
from this change.

JESConfig includes enough information about the old format to read it
and transform it into the new format, after which the new .properties
file will be used automatically.

Also, some code was added to JESProgram to report load errors and
migrated settings.