Highlight better that expression and graphical collection editor are different

Revealed during testing of https://issues.redhat.com/browse/DROOLS-4698

We need a way to tell a user that using the guided editor, you can only add one ore more check to the collection as list of conditions while in the expression user can write whatever he wants so the semantic is completely custom.

Suggested solution:

• to explain the difference directly in the popup, somewhere close to radio buttons create/define.

Example:
[1]

[2]

How that works now:
Each element defined in the graphical editor will be considered as a check to perform: the first screenshot means "check if an element equals to 2 exists in the collection" while the expression means "is the list equals to [2] list?"
What expression should be to make test pass:
(2 in ?)