Cleaner log functions

The logging functions now automatically insert `[nodecg/lib/example]` rather than needing it in every log statement. This filename string is instead set when we require the logger; `require(../logger)('blah')` gives all messages the `[blah]` prefix.

I have also changed out log statements to begin with `nodecg/`, with the idea that extensions should get access to our logger with the (automatically set) prefix `[bundleName/path/to/extension.js]`. Adding `nodecg` to our statements should help someone visually filter between system and extension messages quickly.