Add redis caching

[taras]

When a user landed on contributordays.com, there was a slight delay while Fastboot rendered the page. This PR adds page caching with using Redis. I created a free account on redislabs.com which I'm using for Redis hosting.

To get Redis hooked up, I used fastboot-redis-cache which is a middleware that I added in server.js.

redislabs requires a password. fastboot-redis-cache didn't support providing a password, so I created a fork on https://github.com/taras/fastboot-redis-cache/tree/add-password-option and a PR to fastboot-redis-cache

To store password securely, I used git-crypt which automatically encrypt and decrypts server/config.json on checkout and commit. You have to install git-crypt to deploy the server.

I moved all of the configurations into config.json.

[taras]

@jorgelainfiesta did you see this?

[jorgelainfiesta]

@taras yep, it's quite interesting. I'm not very familiar with redis, but I think I got what it does.

[taras]

It's an in-memory key value store. Think of it as a database that only stores data based on key and it's corresponding value. So, foo: bar. You can get('foo') and set('foo', 'some value'). It's very fast because the values are stored in memory. It's intended to be primarily fast and not permanent. You should only put into it values that you're not afraid to loose. The combination of speed and impermanence makes it perfect for caching scenarios.