efl: Change non required constructors to @optional.

Authored by lauromoura on Feb 7 2019, 9:02 AM.


efl: Change non required constructors to @optional.

These constructors aren't checked for in the finalize step of the
initialization and may be given the @optional tag.

For C# this means they can be ommitted from the constructor call.

This also adds Efl.Ui.View.model as a constructor of
Efl.Composite_Model as the finalizer checks for it.

Fixes T7673

Test Plan: make check

Reviewers: segfaultxavi, zmike, bu5hm4n, cedric, felipealmeida

Reviewed By: segfaultxavi, cedric

Tags: efl, DO NOT MERGE

Maniphest Tasks: T7673

Differential Revision: https://phab.enlightenment.org/D7855