Show machine tokens for auto-placed units.

This fixes https://bugs.launchpad.net/juju-gui/+bug/1383381
Please refer to the bug for QA instructions.
Merge pull request #627 from frankban/auto-place-tokens

Show machine tokens for auto-placed units.

This fixes https://bugs.launchpad.net/juju-gui/+bug/1383381
Please refer to the bug for QA instructions.
Tweak how hide/highlight is rendered in MV.
Merge pull request #625 from kadams54/hide-highlight-tweaks

Tweak how machine view renders hidden/faded/highlighted services.

The specs for how hide/highlight should work in machine view:

## Show/hide

* Machine view is a literal translation of hardware so we can't be so clear cut.
* Hiding a service just de-prioritises the service.
* The hidden service is not populated in the machine column.
* The hidden services is de-prioritised in the container column. They sit at the bottom of their respective containers and stack up horizontally, the name of the service is not shown but can be found out via a tooltip which should appear from hovering over the charm icon.
* The machine and containers never get hidden with show/hide.

## Highlight/unhighlight

* Highlighting a service changes the machine column to only show machines which include the highlighted service. This allows users to use it as a filtering tool.
Refactor event handlers into extension.
Merge pull request #628 from kadams54/added-services-db-refactor

Refactor event handlers into extension.

Also wrap tests around the event handlers.