add waterfall mode

[joshh-devrel]

@junjunsong

=======================================

Looking at the waterfall code, it's basically the same as the bidding, except the below class(es) and method(s), but they are using the same listeners:

• Banner: mbBannerView.load(); v.s. mbBannerView.loadFromBid(bidToken);
• Interstital:
  • mbNewInterstitialHandler v.s. mbBidNewInterstitialHandler
  • mbNewInterstitialHandler.load(); v.s. mbBidNewInterstitialHandler.loadFromBid(bidToken);
  • mbNewInterstitialHandler.show(); v.s. mbBidNewInterstitialHandler.showFromBid();
• Native:
  • mbNativeHandler v.s. mbBidNativeHandler
  • mbNativeHandler.load(); v.s. mbBidNativeHandler.bidLoad(bidToken);
• Rewarded:
  • mbRewardVideoHandler v.s. mbBidRewardVideoHandler
  • mbRewardVideoHandler.load(); v.s. mbBidRewardVideoHandler.loadFromBid(bidToken);
  • mbRewardVideoHandler.show(); v.s. mbBidRewardVideoHandler.showFromBid();

=======================================

Therefore, for each ad format, we can just have a base class:

• com/google/ads/mediation/mintegral
  • MintegralBannerAd.java
  • MintegralInterstitialAd.java
  • MintegralNativeAd.java
  • MintegralRewardedAd.java

And have the waterfall and bidding classes extend from it (in two different waterfall and rtb directories`:

• com/google/ads/mediation/mintegral/waterfall
  • MintegralWaterfallBannerAd.java
  • MintegralWaterfallInterstitialAd.java
  • MintegralWaterfallNativeAd.java
  • MintegralWaterfallRewardedAd.java
• com/google/ads/mediation/mintegral/rtb
  • MintegralRtbBannerAd.java
  • MintegralRtbInterstitialAd.java
  • MintegralRtbNativeAd.java
  • MintegralRtbRewardedAd.java

See how we do it in another adapter:

• Base class
• Bidding class
• Waterfall class