base: don't allow selecting draft currencies by default

The initial intention was to "disallow invalidated", without forcing users to
validate everything, but it was probably a mistake, if users don't need to
validate then validation workflow would be a bit meaningless.

This is made after an incident where a user mistakenly cloned a validated
currency and the cloned currency was available everywhere in the system.

Change to not return draft currencies by default and also change so that all
items are tuple, for consistency. That should have no impact and is a bit
easier for the test.

Also adjust accounting_ui_test, we need to validate currencies for the tests
and clear cache if we validated some (but we don't need to clear cache if we
validate accounts, because account caches is more clever and does not need to
clear all cache)