Channel ID can clash with nodes in hst:sites and hst:configurations

The channel manager is responsible for generating unique channel ID. Currently, these IDs are only different from all other channel ID. However, the channel ID is also used for the names of generated child nodes in hst:sites and hst:channel. When an existing node in there has the same name as the created channel ID, the creation of a channel will fail.

Steps to reproduce:
1. login to the GoGreen test server
2. create a new channel with the name 'common'

Expected: the channel is created succesfully
Actual: creation of the channel fails, because the generated hst:configurations child node for the new channel will be called 'common', and such a configuration node already exists.