Automatically inflect the list of applications

[josevalim]

Therefore, one last proposal is the following:

def application do
  # Any application that does not come from a dependency, such
  # as Erlang and Elixir applications must be explicitly listed.
  [extra_applications: [:logger]]
end

We will also support the :runtime option (or something more appropriately named) for dependencies that allow us to specify a dependency is not necessary during runtime. For example, distillery itself would be specified as:

{:distillery, ">= 0.0.0", runtime: false}

With the features above, the list of applications, when not specified, will be calculated by:

applications = applications || all_non_optional_runtime_apps_from_prod_deps
(applications ++ extra_applications) -- included_applications

/cc @fishcakez

[josevalim]

Closing in favor of #5473.