Multiple viewType support for ShimmerAdapter and some easy access xml attributes

Now you can set xml attributes for shimmer layout reference and number of shimmer to be shown while loading. Also now you can able to change view type of ShimmerAdapter

• New ItemViewType contract to setup viewType for ShimmerAdapter based on layoutType and position, use ShimmerRecyclerView.setItemViewType to set contract.
• Use shimmer_recycler_layout xml attribute to set shimmer layout reference.
• Use shimmer_recycler_item_count xml attribute to set number of shimmer items.