Don't query gravatar everytime a page is loaded

What does this MR do and why?

Puts gravatar fetch into a helper. Stores gravatar for user to help with page load times for users with slower internet. Add user DB field for pfp Futures "offline crafty" efforts where a user will not have long page-load times from loading gravatar until it times out if they have no internet.

Fixes #161 (closed)

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