Show warning in editor when local draft is out of date

[thebaer]

When editing a post, this tracks the updated date that the local, in-browser draft is based on, and compares it to the post's actual updated value in the database.

If the database's updated value is after the local draft's updated date, this warning is shown to the user, allowing them to delete their local draft and load the latest version:

This fixes #41.

Testing notes: This PR includes style changes; update your stylesheet by running: make ui. Also note your database timezone must be set to UTC for this to work correctly.

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[cjeller1592]

Works good on my end!

Would it be worth it to add language mentioning if you want to override the draft updated elsewhere?

This post has been updated elsewhere since you last published! If you want to override that update, then continue with this draft. If not, delete draft and reload.

But that might be such a small use case that I don't think it's worth mentioning.

[thebaer]

Thanks for checking this out, @cjeller1592! I wanted to keep it concise, which is why I chose the current verbiage. But if it's confusing to people we can definitely change it in the future.

Merging this now!