4th fragment added

this is the 4th fragment of the swiped screens
Page horizontal scrolling complete

In this commit i'm finished with the horizontal scrolling among
different level screens.
*future improvements: the navigation bar shouldn't transitions every
time the user swipes. Also change the look and feel
Navigation bar is now placed on a screen fixed point

Previously, as the user was scrolling horizontally between levels the
navigation bar was also scrolling. No it remains always on the bottom
of the screen