Uniform deployment process + migration to new server

I just migrated the blog to the new Digital Ocean machine I just created
No one should notice the migration at all (if you did, something went wrong)

I also finished setting up a more unified deployment process for all of our apps, and this PR is the result of applying that process to our blog, using the new server

A summary of the changes:
* nginx config included in the repo
* uses foreman and .env in production
* uses postgresql in all environments

I also set up semaphore, which will be deployment automatically once this gets merged
That's entirely possible. You can have the `Procfile` setup for development for example, and then `Procfile.production`, `Procfile.staging`, etc

But in those cases you'll have to also configure Capistrano to point to the correct one:

```ruby
set :foreman_options, {
  procfile: "Procfile.#{fetch(:stage)}"
}
```

Since this project doesn't have a staging server, and we don't really need a procfile for development (`rails s` is enough here), I didn't bother with that here