[general] create/select missing icons

I'm afraid the list of icons in CMS7-8548 was not complete.

For the other sections in the "Content" and "Channel" perspectives, the following icons are need to be created or selected from the set we have. For each of the sections, below a list which items still are missing:

• Images
  • "Add image..." (note the slightly different background from "Add document..."
• Assets
  • "Add file..." (currently the same as "Add image..."
• Configuration
  • "Create namespace..."
  • "Add document type..."
  • "Add compound type..."
• While editing a document type icons are needed for:
  • Tab
  • "Edit"
  • "Copy"
  • "Commit"
  • When editing, there are also icons for "Save" and "Done" I suggest we reuse "Save" and "Save & Close" from the normal documents
• Channels:
  • Big icons for the channel overview
  • Experiments icon (see screenshot)

See screenshots for current icons