#25 Toggle icon settings in tl_metamodel_attribute -> tl_metamodel_dcasetting (state: open)

Issue description

As an addendum to #12.

We should move the following settings from tl_metamodel_attribute to tl_metamodel_dcasetting:

• check_publish
• check_inverse
• check_listview
• check_listviewicon
• check_listviewicondisabled

see #26