Implement plugin for verbose builds

[Dominik Braun]

Since verless highly attaches importance to build performance, there's no info-level logging when running a build. However, the difference between a non-logging and a logging build is not relevant for many, if not most users.

To solve this problem, we should provide a verbose plugin that enables verbose builds with some informational logging, deprecation warnings etc. We even may recommend this plugin by default.

Why a plugin instead of a simple -v flag and a logging level?

First, -v has to be stated with each build command. We could solve this by adding a verbose: true field to the configuration's build section, but there also another reason:

This is not only about pure logging. Classical logging with multiple levels and printing log messages only if the level matches is not sufficient here, because we will need to perform some analysis on the project to enable more advanced log messages. For example, the verbose plugin will need to check if there's a css or js directory manually and then decide whether to print a deprecation warning.