Improved Eclipse support for the Bazel project

Now the paths are 100% determined using Bazel query. To adapt to
another project, change the variables at the top of the
setup-eclipse.sh file. It also handles correctly java_plugins now.

Because we must do queries on the full workspace, it is not easy to
embed in a bazel build. I made a prototype for it but it is really
impractical.

--
MOS_MIGRATED_REVID=91580472
diff --git a/.gitignore b/.gitignore
index cf4d5da..98f085e 100644
--- a/.gitignore
+++ b/.gitignore
@@ -7,6 +7,7 @@
 /.settings
 /.project
 /.classpath
+/.factorypath
 /fromhost/
 /base_workspace/bazel-bin
 /base_workspace/bazel-genfiles