Make app repository url configurable

[a-maze-d]

Currently the app repository url is hard coded. This makes it impossible to show the correct banner in the nerves_livebook version, resulting in this issue

Why not make the app repo url configurable? This is a small change (as long as the approach is the same, i.e. github is the repo, the versioning semantics are the same, ... which are reasonable as a first step)

I'm happy to raise a PR with the proposed changes

[a-maze-d]

I raised a PR as a proposal

[a-maze-d]

Even though the PR has been committed, it turns out that's just part of the story. The issue is that Livebook.Config.app_version/0 has a hard coded version (picked from the Mix.Project.config/0 at compile time).

We need to distinguish between "Livebook the library" (that can be used/embedded in other applications, and "Livebook the application" (that can be executed). My proposal is to make this distinction also on a code level by:

1. introducing a LIvebook.Config.livebook_verision/0 that corresponds the version of the library and hence can be taken from the Mix.Project.config/0.
2. change the Livebook.Config.app_version/0 to pick up the version as reported by Application.get_env/3 and use the Livebook.Config.livebook_version/0 as default.

The new code would look like the following:

@livebook_version Mix.Project.config()[:version]

  @doc """
  Livebook can be used as both an application as well as a library embedded
  in other appilcations. This function always returns the version of the library
  """
  def livebook_version(), do: @livebook_version

  @doc """
  Returns the current version of the running Livebook application. Note: this version
  can be different from the livebook_version when livebook is used as a library.
  """
  def app_version(), do: Application.get_env(:livebook, :app_version, livebook_version())

I'll raise a new PR

[a-maze-d]

PR raised

[a-maze-d]

Thanks to the feedback, we changed the solution, but the basic changes are in :-) Thanks to all involved