Resolve default package definitions if extact version is unavailable.

Old behavior can be reverted by setting up a dependency_resolvers_conf.xml with the following contents

```
<dependency_resolvers>
  <tool_shed_packages />
  <galaxy_packages />
</dependency_resolvers>
```

The new behavior corresponds to the following dependency_resolvers_conf.xml contents:

```
<dependency_resolvers>
  <tool_shed_packages />
  <galaxy_packages />
  <galaxy_packages versionless="true" />
</dependency_resolvers>
```

Still think galaxy_packages should come before tool_shed_packages in resolution order so that deployers can fix broken tool shed installs with manual installs or deploy optimized versions of packages without having to mess with a dependency_resolvers_conf.xml file.
Reduce extra-module dependencies in galaxy.tools.deps.

Eliminte older elementtree dependency. Eliminate dependency on galaxy.util:string_as_bool. Only remaining dependency in galaxy.util.submodules.

PEP-8 fix up galaxy.util.submodules so it can be copied directly into the LWR.

This will ease adding the whole module and submodules to LWR for remote dependency resolution.
Refactor command_factory:build_command to reduce parameter count.

Grouping all parameters to tweak the building of this command line for remote servers (read LWR) - since I have at least one more to add.
Allow new dependency_resolution destination for LWR runner.

It can be 'none', 'local', or 'remote'. At this point this allows one to disable command dependency injection if set to 'none' or 'remote'. Actually implementing logic for 'remote' resolution will follow.

In subsequent changes - 'remote' will make backward-imcompatiable API calls to the LWR - this is why 'none' is also provided as an option - it will be backward compatiable way to disable dependency resolution for an LWR destination.
command_factory cleanup - fix very poorly named input parameter.
command_factory cleanup - introduce abstraction for more readable command construction logic.
Add more unit tests for command_factory.

In particular for for task splitting commands and copying work dir outputs.
command_factory cleanup - split big build_command method into smaller well-named pieces.
command_factory cleanup - a couple more small tweaks for readability.
Implement 'remote' dependency_resolution for LWR.

Set LWR destination parameter 'dependency_resolution' to remote. This will disable all dependency resolution on Galaxy side when building up command line and instead pass the tool's requirements along to the LWR server for resolution on that end. This requires a very up-to-date LWR server.

I think right now 'galaxy_packages' and 'modules' resolution would work but not 'tool_shed_package' resolution - I think more repository information related to the tool needs to be passed along to the LWR to enable this.

Updates the LWR client code through LWR changeset 4380e65 - mostly bringing in changes to enable this but also includes other small refactorings to stager.py.
Fill out job_conf.xml example with LWR options added over recent months.