SYSML16 — Incorrect constraint [2] on InterfaceBlock

Constraint [2] specifies that "Interface blocks cannot have composite properties that are not ports". However, in order to show FlowProperties, typed by ValueTypes and owned by InterfaceBlocks, you need to be able to have composite properties.

The constraint at the moment is too strict and needs to be changed to allow certain composite properties.

Reword constraint#2

Modify constrain#2 as suggested and in order to merge with issue SYSML16-455 as well, as part of SYSML16-274:
Revised text:
Interface blocks' composite properties are either ports, value properties or flow properties_