IGV incomplete gitignore

After a complete clean and fresh build of IGV, running `java -Xcomp -XX:PrintIdealGraphLevel=5` results in the untracked generated files below:
```
Untracked files:
  (use "git add <file>..." to include in what will be committed)
src/utils/IdealGraphVisualizer/all-clusters.dat
src/utils/IdealGraphVisualizer/all-files.dat
src/utils/IdealGraphVisualizer/all-installer.dat
src/utils/IdealGraphVisualizer/all-layers.dat
src/utils/IdealGraphVisualizer/all-local-layers.dat
src/utils/IdealGraphVisualizer/all-manifests.dat
src/utils/IdealGraphVisualizer/all-modules.dat
src/utils/IdealGraphVisualizer/all-resources.dat
src/utils/IdealGraphVisualizer/lastModified/
src/utils/IdealGraphVisualizer/localeVariants
src/utils/IdealGraphVisualizer/package-attrs.dat
```

We should add these generated files to the IGV `.gitignore`.