Weakref over clone

[kenz-gelsoft]

This rewriting is not trivial and is not great as I thought.

• Sizers are not wxTrackable. So another approach is required for them.
• Many samples have structs which hold multiple widgets. Check if destroyed when accessing them everytime is safe but too complicated.

wx::Window-derived structs(that behaves like pointer to them) won't Drop(), so purpose of this rewriting is consistency to non-Window wx::Objects' lifetime.

Rewriting to unowned version of binding struct is enough.

[kenz-gelsoft]

Note to myself

• impl Clone just for OWNED=false variants
• and use them to hold wx binding in struct to be Cloned on simple case.

[kenz-gelsoft]

Consider keep wx::Windows Clonable as they don't have Drop impl(effectively they are not smart ptr).

This should reduce almost boilerplate code introdubed in this PR.

[kenz-gelsoft]

Splitted to following PRs. closing...

• 151

• 152

• 153