Mixin Channel Info classes does not result in 'editable channel settings'

Hey wko,

is it possible that you take a look at this since it seems to me unfinished work of HSTTWO-4321. What I noticed is the following:

When specifying only hst:channelinfomixins and no hst:channelinfoclass, then the 'settings' button below Channel in the channel mgr is grey and cannot be opened. Only when adding an explicit hst:channelinfoclass, the settings button becomes enabled.

AFAIK, the settings button is enabled based on

org.onehippo.cms7.services.hst.Channel#channelSettingsEditable

However I do not see this used in the channel mgr code. the only part that differs between the serialized channel object between with and without hst:channelinfoclass is:

channelInfoClassName