Use camel case for config file

[istreeter]

This is a breaking change

Currently our config file uses a mixture of hyphenated keys (e.g. repo-server) and camel case keys (e.g. maxPoolSize). Furthermore, we are trying to unify all snowplow/iglu applications to use a similar style of configuration.

I know this is an inconvenient change for users who upgrade from 0.6.x to 0.7.0, but I believe now is the right time to make this change, and a consistent config style will ultimately be beneficial to users.