Manages imported modules and protects against concurrent imports.
Keeps lists of all imported Python modules and templates as well as other
config files used by Webware for Python. For modules which are not directly
imported, ImportManager can use ImportSpy to keep track of them. This can
be used to detect changes in source files, templates or config files in order
to reload them automatically by the AutoReloadingAppServer. The use of
ImportSpy can be suppressed with the``UseImportSpy`` setting.