Show progress when saving config

[yuvipanda]

Our first 'user test' left us with a lot of very useful comments (thanks @zaneselvans!). A primary theme here is that we don't actually display any progress when you save your config. No state changes, no spinners, etc. Very confusing!

TODO

• Make it clearer that you need to hit the 'submit' button to save your changes
• Show indication of saved state - 'needs saving', 'saving', 'saved!'
• If save fails, provide a decent error message