adding several improvements to the visual design

Feel free to criticize :)
1. mouse over on the history graph is linked only to rectangles
2. changing the mouse icon over text in the forcemap layout
3. using rounded rectangles in forcemap
fixing click to center on history chart
fixing click to center on forcemap
adding ability to drag the force map
Merge branch 'vis-improvements'
reenabling centering
Merge pull request #3 from XDATA-Year-2/vis-improvements

adding several improvements to the visual design