docs: Updated Building your First App tutorial. Bug: 13429905

-Updated default code in activities from ADT
-Updated screenshots for ADT wizards when changed
-Updated activity_ with fragment_ where required
-Other minor changes

Stage: http://quixote.mtv:8004/training/basics/firstapp/creating-project.html

Patch: Removed border from the new ADT screenshots.
Patch: Replaced device screenshots using an Android 4.4 device.
Patch: Addressed Katie's comments.

Change-Id: Ic0acf714b1b5913f1f82d6eafac53666a721dfe4