Add TokenSource.Property

[iRevive]

The aim of the PR is to solve IntelliJ IDEA importing issue.

IDEA correctly picks up properties from .sbtopts file and therefore can download dependencies from the GitHub maven repository.

Partially solves #24, #26, and #42.

[necosta]

Hi @djspiewak , can we merge and publish this change?

Was debugging an issue with IntelliJ and was thinking the exact same solution as @iRevive suggests here.

Many thanks.

[necosta]

Nice to Have. A Or method with the three parameters.

[iRevive]

Two parameters should be enough:

val source: TokenSource = TokenSource.Environment("TOKEN_1") || TokenSource.GitConfig("config") ||  
TokenSource.Property("PROPERTY_TOKEN") || TokenSource.Environment("TOKEN_2")

Encoded as:

val source: TokenSource = TokenSource.Or(
  TokenSource.Environment("TOKEN_1"),
  TokenSource.Or(
    TokenSource.GitConfig("config"),
    TokenSource.Or(
      TokenSource.Property("PROPERTY_TOKEN"),
      TokenSource.Environment("TOKEN_2")
    )
  )
)

[necosta]

Yes, good point. That would work.

[er1c]

@iRevive I stole part of this idea for https://github.com/er1c/sbt-github/pull/2/files is that ok? it was interesting to work through some of the sbt tests, you have to nest a project/project/plugins.sbt to import the plugin, and then set the githubTokenSource in the project/plugins.sbt to override the resolver chain to resolve a github repo - publishing is more bespoke and easier

[iRevive]

@er1c no worries. I'm glad my changes are used for good :)