This commit reorganizes the package structure. The gvaldap.settings
modules have been merged. The gvaldap.ldaptasks module has been move up
one level to have task names without the gvaldap prefix.
isort control instructions have been added to setup.cfg.
This commit updates the Django dependency version to 1.9.2 and gvacommon
to 0.3.0 that provides gvacommon.settings_utils.get_env_variable. The
gnuviechadmin.settings.base module now uses this implementation instead
of an own copy and the corresponding test has been removed too.