replace meteor/jparker:gravatar with our ReactionAvatar react component

[kieckhafer]

Resolves #2410

In our effort to move away from meteor packages, this update replaces meteor/jparker:gravatar with ReactionAvatar, our React version of Gravatars, throughout the app.

Most of the app has already been done, so this PR specifically replaces the Gravatar's in the nav bar, and inside the Groups table (when logged in as an admin).

[brent-hoover]

I get this error when starting up

modules.js?hash=7ee907e6d17784321fe48b45f09bcaa0f5d0b366:85730 Warning: Failed prop type: Invalid prop `userImage` supplied to `Reaction(MainDropdown)`.
    in Reaction(MainDropdown) (created by Tracker(Reaction(MainDropdown)))
    in Tracker(Reaction(MainDropdown)) (created by withProps(Tracker(Reaction(MainDropdown))))
    in withProps(Tracker(Reaction(MainDropdown))) (created by Tracker(withProps(Tracker(Reaction(MainDropdown)))))
    in Tracker(withProps(Tracker(Reaction(MainDropdown)))) (created by Reaction(NavBar))
    in div (created by Reaction(NavBar))
    in Reaction(NavBar) (created by Tracker(Reaction(NavBar)))
    in Tracker(Reaction(NavBar)) (created by Reaction(coreLayout))
    in div (created by Reaction(coreLayout))
    in Reaction(coreLayout) (created by Route)
    in Route
    in Switch (created by Reaction(App))
    in div (created by Reaction(App))
    in Reaction(App) (created by Tracker(Reaction(App)))
    in Tracker(Reaction(App))
    in TranslationProvider (created by Tracker(TranslationProvider))
    in Tracker(TranslationProvider)
    in Router (created by BrowserRouter)
    in BrowserRouter

[brent-hoover]

Getting a console error on startup

[kieckhafer]

@zenweasel updated to fix the error