Addition of IManager to standardize SDK interfacing classes

[angel-ayala]

I would like to discuss the necessity of a IManager class to define the common structure for the manager classes of each SDK's component. For now I only see mInstance and retrieveMetaData() as common elements among the components by inheriting from dji.sdk.base.BaseComponent.

[TimonSchreiber]

I do think that a common interface for the manager classes is a good idea, but not because of tidiness, instead it will be necessary if we ever want to add support for msdk5. Then we will need a common interface to program against which all managers use.

mInstance and retrieveMetaData() are not ideal for common properties, the later is only used by CameraManager and exposing a BaseComponent-typed property on the interface ties it directly to the DJI SDK, which undermines its usefulness as an abstraction layer for dual MSDK support.

A reasonable interface might look like this:

interface IManager<T : BaseComponent> {
    fun init(component: T)
    fun isConnected(): Boolean
}

[angel-ayala]

That's a really good observation, that seems to be the proper way, for now I don't see the urgency in addressing this, but if other major changes appears moving towards MSDKv5 or anything related to the API can be discussed here to define the future action plan.

[angel-ayala]

As discussed in #64 , something similar must be considered in this refactor for handling the API results.