Support maven_install and jvm_import style dependencies

[plaird]

As a Spring Boot rule new user
I would like to have an organized list of Maven dependencies to add to my WORKSPACE
Such that adding Spring Boot is not a painful ordeal.
Such that I can use Bazel 2.0 without issue (no use of maven_jar).
Such that I can use maven_install or jvm_maven_import_external

The problem is seen by looking at https://github.com/salesforce/bazel-springboot-rule/blob/master/external_deps.bzl
It is a mess.

This needs to worked in conjunction with the import bundles work item:
#4

To achieve this, we need to also migrate to this standard:
https://docs.bazel.build/versions/master/skylark/deploying.html

[plaird]

I have a version that ported this to maven_install, I will post shortly.

[plaird]

This was done in September.

[plaird]

I am reopening - we had a lot of cruft in the import bundles concept left from maven_jar. I am cleaning that up.