Add Mounting utility component

[TrySound]

No description provided.

[renatorib]

Older discussion about this: #41

[renatorib]

Personally I like the idea. But Idk if it fits the 'powerplug' concept of state containers. It's don't have any state.

[TrySound]

@renatorib Well, it has. :)

[TrySound]

@renatorib From mount to unmount it passes state.

[renatorib]

Not exactly. In your example you use Value to handle the state and not Mounting component itself. See, I'm not saying it's not useful, I really liked it. I like the idea of wrapping some lifecycles like that. But I do not see it fit into the lib, this does not even return a fn callback, it would not be possible to use with compose, for example.

[TrySound]

Okay. Let's leave it for further discussions. I'll try to fit the idea to powerplug.

[TrySound]

@renatorib I found some solution. We can extend mount/unmount callbacks with refs which are rely on them.

[TrySound]

And it's stateful. However we still need another component like Value or State, but it's like different type of state.

[renatorib]

I was thinking yesterday and I have some ideas in my head. When I mature the idea I'm going to create a discussion issue here. Meanwhile I'll leave this PR open.

[TrySound]

I don't support this idea anymore. It's better to prefer lifecycle with class. Lifecycles in opposite to state containers do not introduce any functionality and may lead to many learning issues. Also 16.4 will introduce new stateful component api which will be in a way more elegant.