Allow hidden items in the input-model

[mgsstms]

Allow the option to have the hidden items in the in the input array.

We will need to define the extra parameter 'hiddenProperty' (true/false). It will help us to avoid to pass the filtered array to the multiselect (and keep 2 copies of input array) or use filtering (which is running each digest cycle and affect the performance).

[alexandernst]

Could you explain a little bit further? How exactly do you want this feature to work?

Let's say you have the following structure:

A
    B
    C <--- hidden
    D
E
    F
    G <--- hidden
H
I <-- hidden
J

What should be shown in the select? What should the output model contain if I select A?

[mgsstms]

Select should show this:

A
    B
    D
E
    F
H
J

If you select A, the output model will be the same as now (only no without 'C')