Variety of improvements

- Rename sources to distfiles for clarity.
- Per sys(a/c) distfiles to reduce rootfs.py processing and reduce RAM
  usage in sysa.
- Canonicalise early kaem mes/tcc files to kaem script conventions.
- Cleanup unused setup in python.

.gitignore

@@ -5,6 +5,7 @@
 
 tmp/
 kernel
-sources/
+sysa/distfiles/
+sysc/distfiles/
 __pycache__
 sysa/bootstrap.cfg