Improve binding to member functions

[RippeR37]

Improve logic when binding to member functions. This may include, but is not limited to:

• requiring explicit base::Unretained() when binding to raw pointers
• better interoperability (and easier to maintain code) when binding to base::WeakPtrs
• potentially allow binding to std::shared_ptr<T> (as a replacement of scoped_refptr<T>)
• consider also other adapters - both for class pointer and also for arguments (e.g. like base::Owned)

[RippeR37]

Done. For argument adapters - created separate issue (#15).