Gradle lockfile parser: track "Project" names so we can interpolate them when needed later.

[tiegz]

It looks like gradle dependencies will sometimes output a project as a dependency without a name:

+--- project :

The most logical explanation is that the emptiness implies the current project's name, so we can interpolate that if we start tracking it.

Followup to https://github.com/librariesio/bibliothecary/pull/559