reorg: reorganize fixtures in test_controller.py

No code changes, just bringing fixtures into test class that uses them
instead of having them distractingly appear first in the file where the
reader has to hunt for the actual test classes.
ctrlr: add prettify step to extract command
reorg: reorganize fixtures in test_model.py

No code changes, just bringing fixtures into test class to improve
readability.
model: add Package.prettify_xml()
model: add PkgItem.prettify_xml()
accept: add explicit manifest for pretty extract