Implemented basic swipe fragment demo

There are 3 fragments SwipeDemoAFragment, SwipeDemoBFragment,
SwipeDemoCFragment that are contained in the SwipeDemoActivity.
The swipe demo activity controls the sequence in which the fragments are
shown by either swiping left or right.

Modified swipe_demo_activity.xml to be a ViewPager.
Modified SwipeDemoActivity.java to use android.support.v4.* as per
required by the ViewPager class.

Added xml and fragment.java files for 3 swipe demo fragments.