Have placeholders for all UI elements and load them asynchronously

[basshelal]

This is hard, but worth it, start it with BoardView. Essentially we want any UI element to have a simple initial placeholder look while we load, bind or finish its initialization code on a background thread. In the context of BoardView we can change the onBindViewHolder of BoardView and TaskListView especially such that they both show some simple placeholder and then when the data is loaded and everything is set up on a background thread, we can show that new stuff. This will make the experience faster and smoother overall.

[basshelal]

This is done, the slowness is because of all the code in onBindViewHolder we'll move that to issue #58