Changes methods/properties visibility to be able to customize specialized GraphView
GraphView is a RealtiveLayout instead of a LinearLayout

To make vertical/horizontal labels more adaptable. This is the first
step to be able to place labels on top/below/left/right from the Graph
in an easy way.
Changes android target API from 16 to 17
Remove unnecessary imports
Remove unnecessary usage of 'this'
Fixes vertical labels aligment bug when setting ALIGN.CENTER

When setting GraphViewStyle.setVerticalLabelsAlign(Align.CENTER) the
text was infact aligned but the width of the TextView wasn't being
recalculated.
Merge pull request #1 from kalemontes/FollowCustomGraphView

Changes made for Follow custom graph view that can be really useful.