Added gradlew and two fixes

Hey.

Remade my master branch for this pull request, so don't pay attention to the commit dates (first commit is newer than the other two).

This PR consits of three commits:
1) Added gradlew to the project. It makes checking out and building on-the-go much easier. I hope you don't mind this commit, but if you do, close this PR and I'll make a new one without this.
2) Change to miner's logic to use the harvest level reported by tools themselves, not their material. This fixes #45.
3) Setting extDirection to DOWN in TilePlanter's constructor. This fixes #36.