A simple widget that displays numeric variable values changing in time

Related issue: openworm/org.geppetto#44

A simple widget that displays a table of numerical values of added variables that change in time.
USAGE:

G.addWidget(Widgets.VARIABLEVISUALISER)
VarVis1.addVariable()
...
VarVis1.addVariable()
// it's also possible to rename variables
VarVis1.renameVariable("", "")
Frontend stuff is not my strongest point, so don't expect much from the "look&feel" of this widget. Probably its CSS needs more love.

That's how it looks like now: https://www.dropbox.com/s/4ztydkc3rn0p0sl/Screenshot%202014-09-27%2000.37.36.png?dl=0