1) Added new apis: createInstanceGroup, updateInstanceGroup, deleteInstanceGroup, listInstanceGroups
2) Group can be created using:
* createInsanceGroup api
* deployVirtualMachine/updateVirtualMachine commands (we create a group with name equal to "group" parameter value if the group doesn't exist already)
3) Group can be removed by:
* deleteInstanceGroup api
* when corresponding account is removed
4) Vm can be assigned to one group only. To move vm from one group to another, use updateVirtualMachine command with "group" parameter
5) Changed listVirtualMachines command to use "groupId" parameter instead of "group".
status 6177: resolved fixed
