Add Eclipse project name to build.gradle

This is another way to fix Eclipse project name as it's required that the project name match directory name so that it can be imported directly as a gradle project into Eclipse.

As it has been discussed in PR #346, we want to preserve artifact names.
As per https://github.com/GlowstoneMC/Glowstone/commit/1fa24a7bf6c2fc555217aa8e79dd3f74647170d3, this should be in lowercase.