Disable drag-drop in Browse mode

[VWoeltjen]

Drag-and-drop composition (e.g. from the tree to a Layout) should not be active in Browse mode; this is considered an "editing" activity and should only work from Edit mode.

The exception to this is folders; dragging-and-dropping into the items view of a Folder SHOULD result in adding an object to that folder's composition, even in Edit mode.

Currently, however, drag-and-drop functions for any view that support drag-drop composition, regardless of current mode (Browse or Edit.)

[VWoeltjen]

Some notes for implementing this:

• domainObject.hasCapability('editor') is the useful check to determine if we are in Browse or Edit mode
• The composition part of drag-and-drop is implemented by DropGesture, in platform/representation