GUI-195: Launch Instance Wizard Redux

Implements fixes based on UX feedback for https://eucalyptus.atlassian.net/browse/GUI-195

Includes…
- Selective display of summary area
- Add a "No preference" option for the availability zone selector (Euca only)
- Left align checkboxes in step 4 of wizard

To be implemented in a separate pull request…
- Filters for image picker (probably going to open a new ticket for this since it applies to the Launch Configuration wizard as well)
- Cancel button (awaiting discussion with @JMoLo )