Fixed Gradle linting

Summary: Fixed the linter for Gradle projects. In addition to plain not being broken anymore, it will now also detect individually which modules in a gradle project have been modified and will lint them each individually. This means that non-modified modules (which are often libraries) won't be linted every time. Since the linting is at the module level now, modules with many flavors will also lint significantly faster.

Test Plan: Lint a Gradle project and an Eclipse project.

Reviewers: mbishop, mportune, jstarke

Reviewed By: jstarke

Subscribers: mbishop

Maniphest Tasks: T3591

Differential Revision: https://devportal.imobile3.com/D11064