Refactor MarketWarning component

[drewcook]

Tech Debt

Refactor the <MarketWarning /> component to return an empty JSX tag when the network being passed in is not in a maintained 'frozen markets' list. Currently, in all theimplementations across the UI, there are additional checks against the market name on if it should be rendered or not. This logic should be, instead, moved and contained within the MarketWarning component itself.

Furthermore, consider renaming the component to FrozenMarketWarning, since that is what it is primarily doing. If there is ever a need to expand to other "global market-based warnings", then this component can be renamed back to MarketWarning and expanded upon.

[Jdecristi]

@defispartan did you fix this in pr #1141?