validate feature names do not have whitespace
add dependent:destroy to feature associations
display non-link 0 for flaggable flag counts if feature isn't persisted
Revert "display non-link 0 for flaggable flag counts if feature isn't persisted"

This reverts commit f10cef60d79f02bb1c13851f6dcd3fd78c81c274. With that commit,
there was actually no way to set flag-ins or opt-outs for a feature that hadn't
been persisted.
make FlaggableFlagsController create features if they don't exist