Replace React with Preact

[eduardoboucas]

There is no reason why we couldn't use Preact instead of React for the dashboard, given that it's such a simple application, and I'd really like to see the reduction in bundle size.

Any takers?

[danielbayerlein]

@eduardoboucas I can take the issue if you have not started yet.

[eduardoboucas]

@danielbayerlein That would be great!

[danielbayerlein]

@eduardoboucas See #29, I have two known issues after switch. Will try to solve it.

[ghost]

https://github.com/developit/preact-compat

[ghost]

Will be even faster with full Preact, if that's desirable. Graphs here: https://hackernoon.com/10-things-i-learned-making-the-fastest-site-in-the-world-18a0e1cdf4a7