src: transform all old `writable` in annotations

So just insert an `is`, and move it after the initial value if any.

~~~
sed -i '/ is /!s/\(\( redef\)\?\( protected\)\? writable\)\(.*\)/\4 is\1/'
~~~

The following commits disable old-style attributes and setters in modelize_rpoperty to prevent any reintroduction of them.

This prepare a future PR where old-style attributes and setters are removed from the parser.

Close #280