OPENDJ-3203 Control-panel: creating a new base dn does not complete

This problem exists since we added support for the pluggable backend in the control-panel.
The problem is that when the server is running, the control-panel should issue commands to the running server.
Instead it executed the logic to create the backend when the server is offline.

NewBaseDNPanel.java:
In createBackendOnline(), call the newly added BackendCreationHelper.createBackendOnline().
Removed addBackendDefaultIndexes() (duplicate of BackendCreationHelper.addBackendDefaultIndexes())
 (it was trying to create the indexes twice)
Remove displayCreateAdditionalIndexesDone() (duplicate of printTaskDone())
Moved the code printing the equivalent commands from updateConfiguration(On|Off)line()
 directly inside performTask() to avoid duplication.

BackendCreationHelper.java:
Added createBackendOnline().
Renamed DefaultIndex to CreateIndex.
Added toString()