Avoid double-negative logic

I find 'unless X disabled' harder to comprehend than 'if X enabled'
Disable tag showing if feature disabled

Although in theory people should not have any tags if the feature is
disabled, it feels cleaner to explicitly disable the display code using
the feature flag as well.
Merge pull request #8 from ministryofjustice/tagging-feature-flag-tweaks

Tagging feature flag tweaks