Add state persistence and Helix API support

Changes:

ClipsTime! had been broken due to Twitch ending support for the Kraken API without adding clip offset timing to the Helix API, which let us know when in IRL time a clip had occurred. ClipsTime! needs this information in order to sort clips chronologically across multiple streams and vods. Thankfully, Twitch added support for vodOffset to Helix, allowing us to restore this tool to functionality.
State persistence across page reloads has been enabled using redux-persist. This may wind up causing problems, but it's too nice not to release. This resolves issue #14 .
Minor GUI improvements.

timfitzzz / twitch-clipcatcher