Copyable classes with bindable properties

[balex89]

This PR follows #3995 issue discussion.

I went with Option 3 for a list of reasons:

1. It uncompromisingly covers all aspects of the issue, including tracking of bindable attributes;
2. It doesn't really affect performance much, if done right (see below);
3. It isn't in fact as ridiculously complicated in terms of implementation as it might seem, once you see that it only adds a wrapper for function that reproduces an object instance.

Impact on performance

Since we modify BindableProperty setter method, i ran a simple test to measure impact on code performance when object is a) initialized and b) updated:

class TestClass:

    x = BindableProperty()

    def __init__(self):
        self.x = 1

    def update(self):
        self.x = 2

init_time = timeit.timeit(lambda: TestClass(), number=1_000_000)
a = TestClass()
update_time = timeit.timeit(lambda: a.update(), number=1_000_000)
print(f'creation: {init_time:.6f} s, update: {update_time:.6f} s')

I ran this test several times for the current and updated BindableProperty implementations and got following average figures:

1. For initialization it adds up to 5% performance time on average;
2. For update it adds ~1% (or less) time on average.

Since a user, aiming to create millions of instances, each meant for binding, will probably face more sever issues for other reasons, the real-life overhead seems to be insignificant.