[MAX] Introduce the Banner Adapter

[YuriyVelichkoPI]

Motivation

This ticket is a part of #400.

Support integration of banner ads.

Objectives

• Implement the MaxAdViewAdapter interface in the PrebidMAXMediationAdapter . Follow this guide for the implementation details.
• [Optional] If it makes sense from the development perspective move all adapter logic into the separate class, i.e. PrebidMAXBannerAdapter and keep the PrebidMAXMediationAdapter as tiny as possible.
• In order to pass the winning bid - use the setLocalExtraParameter method of the MaxAdView class.
• In order to get the winning bid in the adapter use the getLocalExtraParameters property of the maxAdapterResponseParameters in the loadAdViewAd method
• Introduce the util method for determination of the winning ad source based on the bid's targeting keys and ad source parameters.
• Investigate if we can use the same method for matching the targeting keys as in the AdMob adapter. If yes move this method into the SDK and use it in both adapters.
• Using the Mediation API prepare the next examples:
  • Banner 320x50 (MAX) [OK, Adapter] -> InternalTestApp, PrbidDemo
  • Banner 320x50 (MAX) [NoBids, MAX Ad] -> InternalTestApp
  • Banner 320x50 (MAX) [OK, Random] -> InternalTestApp
  • Banner 320x50 (MAX) [Random, Respective] -> InternalTestApp
  • Banner 300x250 (MAX) [OK, Adapter] -> InternalTestApp
  • Banner adaptive banners (MAX) [OK, Adapter] -> InternalTestApp