Various fixes

[metalinspired]

Here is a list of changes I have made (hopefully I did not forget something):

• Dropped support for PHP 7.
• Fixed converting Any element. Since I actually do not need this element I only went so far to make the convertion work when this element is used. It seems to work fine, even wrote a test, but I'll let you be the judge of that.
• Fixed few "visit" methods that were missing Choice and Group as child elements.
• Fixed converting Choice that is inside of a GroupRef that has maxOccurs set to unbounded converted as property of that type instead being an array.
• Fixed properties/methods duplicated in extending class.
• Properties are now protected by default.
• Return type hint is now "static" as some IDEs complain how methods do not exist in extending classes when it is set to "self".
• Added support for "fixed" and "default" values. For "fixed" values, the setter still exists in PHP code but is not present in JMS definition. This was the simplest solution since I did not wanted to mess with PHP inheritance rules.
• Added "strict_types" option to configuration.
• Added types to properties/arguments/return values in some places.

Note that all my work is based on converting XZuFi 2.3.
So far everything seems to work as expected and soon I will be using generated classes and (de)serialization in customer code, which will in it self be a test if I broke something 😄

Oh and another thing, if you run the tests (all of them) it might happen that OTA tests fail but it seems that it is a bug in JMS as one interface defines "parse(): array" but class implementing it returns a string.

[goetas]

oh, this looks actually super great!!
On the other hand looks very hard to review... are your changes "per" commit?
Is there any chance you could split it into multiple pull requests?