Deletable blueprint does not result in deletable channel

A channel can be deleted if it's channel node has the property 'hst:deletable' set to 'true'. A blueprint can also contain a channel node. However, the 'hst:deletable' property of a channel node in a blueprint is not copied to the channel node when a new channel is created. That should happen, so developers can easily mark blueprints as "creating deletable channels".

Steps to reproduce:

1. Start the CMS of the HAP branch 'feature/delete-channel'
2. Login as admin
3. Navigate to 'Channels' and click 'Add channel'
4. Select the blueprint 'Website'
5. Give it a name ('test') and a URL ('http://localhost/test') and click 'Create channel'
6. Edit the new 'test' channel

Expected: the toolbar has a 'Channel' button with a 'Delete' option in the menu
Actual: the toolbar does not have a 'Channel' button

In the console you can see that the node /hst:hst/hst:blueprints/website/hst:channel has 'hst:deletable' set to true, but the node /hst:hst/hst:channels/test does not have this property set.