Mavenize the java aspect a bit more.

First, move the java source to what maven's compiler expects.  Then
use it to compiled both main and test code, & run the unit tests.

We still use maven to resolve jar dependencies using our ./jars
mechanism.  But now we have more complicated command lines to to do,
since we have now "unpithed" mvn.
Automatically update pom version to what's in version.rb

Also make package the default task & break out some rake subtasks.
Have maven create a fat jar.
Rename jar-with-dependencies -> with-dependencies.

Among other things, this affects the final fat jar name.
More maven tweaks.

Don't try to set pom version with maven, it starts yelling about
missing poms.

By having maven make a fat jar and then exploding it into ./classes,
we avoid the need for jars/runtime_classes.

Askari::Packaging.java_classes_dir is a Pathname now.

Update several maven plugin versions a la
`mvn versions:display-plugin-updates`

Inline creating jars/test.classpath into the regular build.  Don't
bother creating any other classpaths.
Ditch ./jars, push test classpath into spec_helpers/test_classpath.rb.
Only cache maven deps in before-ci.