Switch from 'libx' to 'lib', delete all obsolete binaries

Switch from 'libx' to 'lib', delete all obsolete binaries

Because 'cd lib && mvn compile' can now download and (un)zip many
previously SCM-committed third-party dependencies, the following 'lib'
subdirectories have been deleted:
 - ant
 - asm
 - commons
 - jarjar
 - junit
 - regexp
 - saxon
This one is new (but not stored in SCM):
 - jdtcore-aj

For each of them, there now is a .gitignore entry, so as to prevent
developers from accidentally committing the downloaded binaries again.

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>