Merge pull request #45 from clstokes/develop

Added support for retrieving VM list with filter options by tags.
Merge pull request #46 from clstokes/develop

Added filter support to listImages(..) on MachineImageSupport w/ MachineImageFilterOptions.
Added @Nonnull to new method
Added support for creating subnets in data centers/availability zones
Added a convenience abstract VLANSupport object to make migration and implementation easier.
Made subnet taggable
Made the filter options nullable so without args == null filter options
Renamed MachineImageFilterOptions to ImageFilterOptions to represent new naming conventions and added an abstract base class for image support
Added hold on asynchronous operations
Added creationTimestamp field to machine images
Added new machine image formats for CloudStack
Added the ability to associate a machine image with a kernel image
Added a convenience method for tag matching
Added an abstract VM support class
Added some new capabilities to the VMFilterOptions added by Cameron
Minor enhancements
Enhanced the abstract methods