WIP deprecate ClassLoader from tests

Fixes failure of test.aria.core.TplClassLoaderTest

Add back the ClassLoader.CLASS_LOAD_ERROR for backward compat (just in
case) and at the same time, remove all references to ClassLoader in the
test, replacing them with MultiLoader.
WIP autoconvert aria.templates.CSSCtxtManager

fixes failure of test.aria.templates.css.CSSCtxtManagerTest
WIP: using a new version of attester (with support for require in at tests)