Remove unplaced units when removing services.
Make the GUI aware of the new Subordinate info.

After a recent change in juju-core, the subordinate
info is available through the mega-watcher for
services and units. This branch enables the GUI to
fully support this where possible.

Also fixed the code so that uses of "subordinate" vs
"is_subordinate" are consistent.
Test that removing a committed service will remove unplaced units.
Only make one remove call and test update.
Display unit's name as a tooltip for unit icons on a machine token.
Add default value to units model subordinate attribute.
Improve the comments reguarding subordinate support in juju-core.
Merge pull request #560 from huwshimi/remove-unplaced-units-with-service

Remove unplaced units with service

Fixes bug #1368566: when a committed service is removed it should also remove unplaced units and their entries in the changelog.
Merge pull request #561 from huwshimi/unit-tooltips

Machine token unit tooltips

Display units' names as tooltips for unit icons on a machine token.
Merge pull request #558 from frankban/subordinate-in-megawatcher

Make the GUI aware of the new Subordinate info.

After a recent change in juju-core, the subordinate
info is available through the mega-watcher for
services and units. This branch enables the GUI to
fully support this where possible.

Also fixed the code so that uses of "subordinate" vs
"is_subordinate" are consistent.
Do not allow scaling up subordinates in machine view.

Also include a few drive by fixes to docstrings.